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USING IRONPDF

How to create .NET PDF API Using IronPDF

Curtis Chau
Curtis Chau
Updated:

When working with modern applications, .NET developers like yourself may find themselves needing to build a centralized PDF generation service. Whether you're generating invoices, reports, certificates, or contracts, having a dedicated .NET PDF API can be beneficial for efficiently managing PDF files. So how can it improve your PDF generation tasks? It does this through providing consistency, maintainability, and scalability across your desktop and web applications. Never before has it been easier to manage document content, PDF pages, and PDF form fields.

In this tutorial, you'll learn how to build a production-ready PDF API using ASP.NET Core and IronPDF, a powerful .NET PDF library. We'll create RESTful endpoints that can generate PDFs from HTML, merge documents, add watermarks, and handle various real-world PDF generation scenarios in your Web API.

Why Build a Dedicated PDF API?

Before diving into the code, let's understand why creating a dedicated PDF API makes sense:

  • Centralized Logic: All PDF generation logic lives in one place, making maintenance and updates easier
  • Microservice Architecture: Perfect for service-oriented architectures where different applications need PDF capabilities
  • Performance Optimization: Easier to scale and optimize a dedicated service for large PDF files, multiple pages, and dynamic data.
  • Language Agnostic: Any client application can consume the API regardless of programming language
  • Consistent Output: Ensures all PDF documents across your organization maintain consistent document layout, paragraph formatting, and PDF content.

Ready to start building? Download IronPDF's free trial and follow along with this tutorial to programmatically create PDF files in your .NET Framework projects.

IronPDF: The Complete .NET PDF Library

IronPDF stands out as the premier PDF library for .NET developers, offering a comprehensive set of features that make PDF generation in Web API projects straightforward and reliable. It's built on a Chrome rendering engine, which ensures pixel-perfect HTML-to-PDF conversions, often in just a few lines of code. It does all of this while maintaining all styling, JavaScript execution, and responsive layouts.

Key capabilities that make IronPDF ideal for .NET PDF API development:

  • Chrome-Based Rendering: Leverages Google Chrome's rendering engine for converting PDF documents from HTML content accurately, with full support for embedded images and other web assets
  • Rich Feature Set: Supports the editing of new and existing documents with digital signatures, PDF forms, annotations, encryption, compression, and more
  • Create Secure PDF Documents: Manage sensitive PDF content with encryption, digital signatures, and document protection.
  • Multiple Input Formats: Use HTML, URLs, images, and Office documents to create PDF documents
  • Advanced Manipulation: Merge PDF pages, split documents, apply watermarks, create interactive PDF forms, and manipulate PDF files programmatically.
  • Cross-Platform Support: Works on Windows, Linux, macOS, Docker, and cloud platforms
  • Performance Optimized: Async operations, efficient memory management, and fast rendering

How to Set Up Your PDF Document API Project?

Let's start by creating a new ASP.NET Core Web API project and installing the necessary packages.

Prerequisites

  • .NET 6.0 SDK or later
  • Visual Studio 2022 or Visual Studio Code
  • Postman or a similar API testing tool for testing your PDF REST API

Creating the Project

First, let's create the project within which we will build our PDF generation tool.

dotnet new webapi -n PdfApiService
cd PdfApiService

Installing IronPDF

The next step is to add IronPDF to your project via NuGet:

dotnet add package IronPdf

Or, using the NuGet Package Manager Console in Visual Studio:

Install-Package IronPdf

Project Structure

An essential aspect of C# development is maintaining a clean and well-structured project folder. For example:

How to Create Your First PDF Endpoint?

Let's build a simple endpoint that converts HTML to PDF format. First, create the service interface and implementation:

Creating the PDF Service

First, we will add the following to our IPdfService.cs file:

public interface IPdfService
{
    byte[] GeneratePdfFromHtml(string htmlContent);
    byte[] GeneratePdfFromUrl(string url);
}
public interface IPdfService
{
    byte[] GeneratePdfFromHtml(string htmlContent);
    byte[] GeneratePdfFromUrl(string url);
}
Public Interface IPdfService
    Function GeneratePdfFromHtml(htmlContent As String) As Byte()
    Function GeneratePdfFromUrl(url As String) As Byte()
End Interface
$vbLabelText   $csharpLabel

In the PdfService.cs file, we will add this:

using IronPdf;
public class PdfService : IPdfService
{
    private readonly ChromePdfRenderer _renderer;
    public PdfService()
    {
        _renderer = new ChromePdfRenderer();
        // Configure rendering options for optimal PDF generation in .NET
        _renderer.RenderingOptions.MarginTop = 20;
        _renderer.RenderingOptions.MarginBottom = 20;
        _renderer.RenderingOptions.PrintHtmlBackgrounds = true;
    }
    public byte[] GeneratePdfFromHtml(string htmlContent)
    {
        // Generate PDF from HTML using the .NET PDF API
        var pdf = _renderer.RenderHtmlAsPdf(htmlContent);
        return pdf.BinaryData;
    }
    public byte[] GeneratePdfFromUrl(string url)
    {
        // Convert URL to PDF in the REST API
        var pdf = _renderer.RenderUrlAsPdf(url);
        return pdf.BinaryData;
    }
}
using IronPdf;
public class PdfService : IPdfService
{
    private readonly ChromePdfRenderer _renderer;
    public PdfService()
    {
        _renderer = new ChromePdfRenderer();
        // Configure rendering options for optimal PDF generation in .NET
        _renderer.RenderingOptions.MarginTop = 20;
        _renderer.RenderingOptions.MarginBottom = 20;
        _renderer.RenderingOptions.PrintHtmlBackgrounds = true;
    }
    public byte[] GeneratePdfFromHtml(string htmlContent)
    {
        // Generate PDF from HTML using the .NET PDF API
        var pdf = _renderer.RenderHtmlAsPdf(htmlContent);
        return pdf.BinaryData;
    }
    public byte[] GeneratePdfFromUrl(string url)
    {
        // Convert URL to PDF in the REST API
        var pdf = _renderer.RenderUrlAsPdf(url);
        return pdf.BinaryData;
    }
}
Imports IronPdf

Public Class PdfService
    Implements IPdfService

    Private ReadOnly _renderer As ChromePdfRenderer

    Public Sub New()
        _renderer = New ChromePdfRenderer()
        ' Configure rendering options for optimal PDF generation in .NET
        _renderer.RenderingOptions.MarginTop = 20
        _renderer.RenderingOptions.MarginBottom = 20
        _renderer.RenderingOptions.PrintHtmlBackgrounds = True
    End Sub

    Public Function GeneratePdfFromHtml(htmlContent As String) As Byte()
        ' Generate PDF from HTML using the .NET PDF API
        Dim pdf = _renderer.RenderHtmlAsPdf(htmlContent)
        Return pdf.BinaryData
    End Function

    Public Function GeneratePdfFromUrl(url As String) As Byte()
        ' Convert URL to PDF in the REST API
        Dim pdf = _renderer.RenderUrlAsPdf(url)
        Return pdf.BinaryData
    End Function

End Class
$vbLabelText   $csharpLabel

The PdfService handles the core process of converting HTML into PDF. Utilizing IronPDF’s ChromePdfRenderer, this class is set up with sensible defaults like page margins and background rendering to produce a polished final document.

When the controller passes in raw HTML, the service uses IronPDF to render it into a professional-quality PDF and returns the result as byte data, ready to download. Additionally, it can also handle entire web pages by converting a URL directly into a PDF.

Creating the Controller

Now it's time to create the controller for our API. This will provide an API endpoint capable of generating PDF files from HTML. It will then be able to download and save PDF documents to your system for further use or sharing.

// Controllers/PdfController.cs
using Microsoft.AspNetCore.Mvc;
[ApiController]
[Route("api/[controller]")]
public class PdfController : ControllerBase
{
    private readonly IPdfService _pdfService;
    public PdfController(IPdfService pdfService)
    {
        _pdfService = pdfService;
    }
    [HttpPost("html-to-pdf")]
    public IActionResult ConvertHtmlToPdf([FromBody] HtmlRequest request)
    {
        try
        {
            var pdfBytes = _pdfService.GeneratePdfFromHtml(request.HtmlContent);
            // Return as downloadable file
            return File(pdfBytes, "application/pdf", "document.pdf");
        }
        catch (Exception ex)
        {
            return BadRequest($"Error generating PDF: {ex.Message}");
        }
    }
}
// Controllers/PdfController.cs
using Microsoft.AspNetCore.Mvc;
[ApiController]
[Route("api/[controller]")]
public class PdfController : ControllerBase
{
    private readonly IPdfService _pdfService;
    public PdfController(IPdfService pdfService)
    {
        _pdfService = pdfService;
    }
    [HttpPost("html-to-pdf")]
    public IActionResult ConvertHtmlToPdf([FromBody] HtmlRequest request)
    {
        try
        {
            var pdfBytes = _pdfService.GeneratePdfFromHtml(request.HtmlContent);
            // Return as downloadable file
            return File(pdfBytes, "application/pdf", "document.pdf");
        }
        catch (Exception ex)
        {
            return BadRequest($"Error generating PDF: {ex.Message}");
        }
    }
}
Imports Microsoft.AspNetCore.Mvc

<ApiController>
<Route("api/[controller]")>
Public Class PdfController
    Inherits ControllerBase

    Private ReadOnly _pdfService As IPdfService

    Public Sub New(pdfService As IPdfService)
        _pdfService = pdfService
    End Sub

    <HttpPost("html-to-pdf")>
    Public Function ConvertHtmlToPdf(<FromBody> request As HtmlRequest) As IActionResult
        Try
            Dim pdfBytes = _pdfService.GeneratePdfFromHtml(request.HtmlContent)
            ' Return as downloadable file
            Return File(pdfBytes, "application/pdf", "document.pdf")
        Catch ex As Exception
            Return BadRequest($"Error generating PDF: {ex.Message}")
        End Try
    End Function
End Class
$vbLabelText   $csharpLabel

Then, in the HtmlRequest.cs file, we will add this:

// Models/HtmlRequest.cs
public class HtmlRequest
{
    public string HtmlContent { get; set; }
    public string FileName { get; set; } = "document.pdf";
}
// Models/HtmlRequest.cs
public class HtmlRequest
{
    public string HtmlContent { get; set; }
    public string FileName { get; set; } = "document.pdf";
}
' Models/HtmlRequest.vb
Public Class HtmlRequest
    Public Property HtmlContent As String
    Public Property FileName As String = "document.pdf"
End Class
$vbLabelText   $csharpLabel

In the first file, we set up a straightforward API endpoint that turns HTML into a downloadable PDF. When someone sends HTML content to the api/pdf/html-to-pdf route with a simple POST request, the PdfController passes the job of converting it into a PDF to a dedicated service.

Once the PDF is created, the controller hands it back to the user as a ready-to-download file. The request itself is structured using the HtmlRequest model, which carries both the raw HTML and an optional file name for the final document. In short, this setup makes it easy for clients to send HTML and instantly receive a polished PDF in return.

Registering Services

Update your Program.cs to register the PDF service:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
// Register PDF service
builder.Services.AddSingleton<IPdfService, PdfService>();
var app = builder.Build();
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.MapControllers();
app.Run();
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
// Register PDF service
builder.Services.AddSingleton<IPdfService, PdfService>();
var app = builder.Build();
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.MapControllers();
app.Run();
Imports Microsoft.AspNetCore.Builder
Imports Microsoft.Extensions.DependencyInjection

Dim builder = WebApplication.CreateBuilder(args)
builder.Services.AddControllers()
builder.Services.AddEndpointsApiExplorer()
builder.Services.AddSwaggerGen()
' Register PDF service
builder.Services.AddSingleton(Of IPdfService, PdfService)()
Dim app = builder.Build()
If app.Environment.IsDevelopment() Then
    app.UseSwagger()
    app.UseSwaggerUI()
End If
app.UseHttpsRedirection()
app.MapControllers()
app.Run()
$vbLabelText   $csharpLabel

How to Handle Different Response Types?

Your API should support different ways of returning PDFs based on client needs:

[HttpPost("generate")]
 public IActionResult GeneratePdf([FromBody] PdfRequest request)
 {
     var pdfBytes = _pdfService.GeneratePdfFromHtml(request.HtmlContent);
     switch (request.ResponseType?.ToLower())
     {
         case "base64":
             return Ok(new
             {
                 data = Convert.ToBase64String(pdfBytes),
                 filename = request.FileName
             });
         case "inline":
             return File(pdfBytes, "application/pdf");
         default: // download
             return File(pdfBytes, "application/pdf", request.FileName);
     }
 }
[HttpPost("generate")]
 public IActionResult GeneratePdf([FromBody] PdfRequest request)
 {
     var pdfBytes = _pdfService.GeneratePdfFromHtml(request.HtmlContent);
     switch (request.ResponseType?.ToLower())
     {
         case "base64":
             return Ok(new
             {
                 data = Convert.ToBase64String(pdfBytes),
                 filename = request.FileName
             });
         case "inline":
             return File(pdfBytes, "application/pdf");
         default: // download
             return File(pdfBytes, "application/pdf", request.FileName);
     }
 }
Imports Microsoft.AspNetCore.Mvc

<HttpPost("generate")>
Public Function GeneratePdf(<FromBody> request As PdfRequest) As IActionResult
    Dim pdfBytes = _pdfService.GeneratePdfFromHtml(request.HtmlContent)
    Select Case request.ResponseType?.ToLower()
        Case "base64"
            Return Ok(New With {
                .data = Convert.ToBase64String(pdfBytes),
                .filename = request.FileName
            })
        Case "inline"
            Return File(pdfBytes, "application/pdf")
        Case Else ' download
            Return File(pdfBytes, "application/pdf", request.FileName)
    End Select
End Function
$vbLabelText   $csharpLabel

Here, we have added a more flexible PDF generation endpoint to the controller. Instead of always forcing a file download, the GeneratePdf method lets the client choose how they want the result returned. This option offers flexibility, allowing PDFs to be displayed in various formats: as a downloadable file, directly in the browser, or encoded as a Base64 string for easy use in APIs.

The request is defined by the PdfRequest model, which builds on the earlier HtmlRequest and adds a ResponseType option. In short, this gives users more control over how they receive their PDFs, making the API more versatile and user-friendly.

Now, when we run our program, we'll see this output on Swagger.

How to create .NET PDF API Using IronPDF: Figure 4 - Swagger UI

How to Implement Common PDF Operations?

Let's expand our service to handle various PDF generation scenarios:

URL to PDF Conversion

[HttpPost("url-to-pdf")]
public async Task<IActionResult> ConvertUrlToPdf([FromBody] UrlRequest request)
{
    try
    {
        var pdfBytes = await Task.Run(() => 
            _pdfService.GeneratePdfFromUrl(request.Url));
        return File(pdfBytes, "application/pdf", 
            $"{request.FileName ?? "website"}.pdf");
    }
    catch (Exception ex)
    {
        return BadRequest($"Failed to convert URL: {ex.Message}");
    }
}
public class UrlRequest
{
    public string Url { get; set; }
    public string FileName { get; set; }
}
[HttpPost("url-to-pdf")]
public async Task<IActionResult> ConvertUrlToPdf([FromBody] UrlRequest request)
{
    try
    {
        var pdfBytes = await Task.Run(() => 
            _pdfService.GeneratePdfFromUrl(request.Url));
        return File(pdfBytes, "application/pdf", 
            $"{request.FileName ?? "website"}.pdf");
    }
    catch (Exception ex)
    {
        return BadRequest($"Failed to convert URL: {ex.Message}");
    }
}
public class UrlRequest
{
    public string Url { get; set; }
    public string FileName { get; set; }
}
Imports System.Threading.Tasks
Imports Microsoft.AspNetCore.Mvc

<HttpPost("url-to-pdf")>
Public Async Function ConvertUrlToPdf(<FromBody> request As UrlRequest) As Task(Of IActionResult)
    Try
        Dim pdfBytes = Await Task.Run(Function() _pdfService.GeneratePdfFromUrl(request.Url))
        Return File(pdfBytes, "application/pdf", $"{If(request.FileName, "website")}.pdf")
    Catch ex As Exception
        Return BadRequest($"Failed to convert URL: {ex.Message}")
    End Try
End Function

Public Class UrlRequest
    Public Property Url As String
    Public Property FileName As String
End Class
$vbLabelText   $csharpLabel

This endpoint lets clients send a URL and get back a ready-to-download PDF of that webpage. When a POST /api/pdf/url-to-pdf request comes in, the controller uses _pdfService to convert the given URL into PDF bytes in the background, then returns them as a file download. If something goes wrong during conversion, it gracefully responds with a clear error message.

Let's try using the URL "https://www.apple.com/nz" and test the POST request. Below is the output we obtained.

Output

How to create .NET PDF API Using IronPDF: Figure 5 - URL PDF output

Adding Custom Watermarks

public byte[] AddWatermarkFromFile(string filePath, string watermarkText)
{
    // Load PDF directly from file
    var pdf = PdfDocument.FromFile(filePath);
    pdf.ApplyWatermark(
        $"<h1 style='color:red;font-size:72px;'>{watermarkText}</h1>",
        75,
        IronPdf.Editing.VerticalAlignment.Middle,
        IronPdf.Editing.HorizontalAlignment.Center
    );
    return pdf.BinaryData;
}
public byte[] AddWatermarkFromFile(string filePath, string watermarkText)
{
    // Load PDF directly from file
    var pdf = PdfDocument.FromFile(filePath);
    pdf.ApplyWatermark(
        $"<h1 style='color:red;font-size:72px;'>{watermarkText}</h1>",
        75,
        IronPdf.Editing.VerticalAlignment.Middle,
        IronPdf.Editing.HorizontalAlignment.Center
    );
    return pdf.BinaryData;
}
Imports IronPdf

Public Function AddWatermarkFromFile(filePath As String, watermarkText As String) As Byte()
    ' Load PDF directly from file
    Dim pdf = PdfDocument.FromFile(filePath)
    pdf.ApplyWatermark(
        $"<h1 style='color:red;font-size:72px;'>{watermarkText}</h1>",
        75,
        IronPdf.Editing.VerticalAlignment.Middle,
        IronPdf.Editing.HorizontalAlignment.Center
    )
    Return pdf.BinaryData
End Function
$vbLabelText   $csharpLabel

Here, we are just manually loading a local file for testing purposes. However, you can adjust this so your PDF API generates a PDF document, and then apply a custom watermark to it with ease.

Watermark Output

How to create .NET PDF API Using IronPDF: Figure 6 - Watermark output from code example above

How to Add Dynamic Data with Templates

For real-world applications, you'll often need to generate PDFs from templates with dynamic data:

[HttpPost("from-template")]
public IActionResult GenerateFromTemplate([FromBody] TemplateRequest request)
{
    // Simple template replacement
    var html = request.Template;
    foreach (var item in request.Data)
    {
        html = html.Replace($"{{{{{item.Key}}}}}", item.Value);
    }
    var pdfBytes = _pdfService.GeneratePdfFromHtml(html);
    return File(pdfBytes, "application/pdf", request.FileName);
}
public class TemplateRequest
{
    public string Template { get; set; }
    public Dictionary<string, string> Data { get; set; }
    public string FileName { get; set; } = "document.pdf";
}
[HttpPost("from-template")]
public IActionResult GenerateFromTemplate([FromBody] TemplateRequest request)
{
    // Simple template replacement
    var html = request.Template;
    foreach (var item in request.Data)
    {
        html = html.Replace($"{{{{{item.Key}}}}}", item.Value);
    }
    var pdfBytes = _pdfService.GeneratePdfFromHtml(html);
    return File(pdfBytes, "application/pdf", request.FileName);
}
public class TemplateRequest
{
    public string Template { get; set; }
    public Dictionary<string, string> Data { get; set; }
    public string FileName { get; set; } = "document.pdf";
}
Imports Microsoft.AspNetCore.Mvc

<HttpPost("from-template")>
Public Function GenerateFromTemplate(<FromBody> request As TemplateRequest) As IActionResult
    ' Simple template replacement
    Dim html As String = request.Template
    For Each item In request.Data
        html = html.Replace($"{{{{{item.Key}}}}}", item.Value)
    Next
    Dim pdfBytes As Byte() = _pdfService.GeneratePdfFromHtml(html)
    Return File(pdfBytes, "application/pdf", request.FileName)
End Function

Public Class TemplateRequest
    Public Property Template As String
    Public Property Data As Dictionary(Of String, String)
    Public Property FileName As String = "document.pdf"
End Class
$vbLabelText   $csharpLabel

For more advanced template scenarios with Razor, Handlebars, or other engines, check out IronPDF's HTML to PDF documentation. You can also explore CSHTML to PDF conversion for MVC applications and Razor to PDF for Blazor applications.

How to Optimize Performance?

When building a production PDF API, performance is crucial. Here are key optimization strategies:

Async Operations

When building projects that involve the use of I/O operations, it is wise to use asynchronous coding. This is especially helpful if your PDF content comes from external resources like:

  • Downloading HTML pages (RenderUrlAsPdf)
  • Fetching images, CSS, or fonts over HTTP
  • Reading/writing files to disk or cloud storage

These operations can then block a thread, but using async prevents your API thread from waiting idle.

Example:

public async Task<byte[]> GeneratePdfFromHtmlAsync(string htmlContent)
{
    return await Task.Run(() => 
    {
        var pdf = _renderer.RenderHtmlAsPdf(htmlContent);
        return pdf.BinaryData;
    });
}
public async Task<byte[]> GeneratePdfFromHtmlAsync(string htmlContent)
{
    return await Task.Run(() => 
    {
        var pdf = _renderer.RenderHtmlAsPdf(htmlContent);
        return pdf.BinaryData;
    });
}
Imports System.Threading.Tasks

Public Async Function GeneratePdfFromHtmlAsync(htmlContent As String) As Task(Of Byte())
    Return Await Task.Run(Function()
                              Dim pdf = _renderer.RenderHtmlAsPdf(htmlContent)
                              Return pdf.BinaryData
                          End Function)
End Function
$vbLabelText   $csharpLabel

Rendering Options

Configure IronPDF for optimal performance:

_renderer.RenderingOptions.EnableJavaScript = false; // If JS not needed
_renderer.RenderingOptions.CssMediaType = PdfCssMediaType.Print;
_renderer.RenderingOptions.RenderDelay = 0; // Remove if no JS
_renderer.RenderingOptions.Timeout = 30; // Set reasonable timeout
_renderer.RenderingOptions.EnableJavaScript = false; // If JS not needed
_renderer.RenderingOptions.CssMediaType = PdfCssMediaType.Print;
_renderer.RenderingOptions.RenderDelay = 0; // Remove if no JS
_renderer.RenderingOptions.Timeout = 30; // Set reasonable timeout
$vbLabelText   $csharpLabel

How to Secure Your PDF API?

Security is essential for any production API. Here's a simple API key authentication approach:

// Middleware/ApiKeyMiddleware.cs
public class ApiKeyMiddleware
{
    private readonly RequestDelegate _next;
    private const string ApiKeyHeader = "X-API-Key";
    public ApiKeyMiddleware(RequestDelegate next)
    {
        _next = next;
    }
    public async Task InvokeAsync(HttpContext context)
    {
        if (!context.Request.Headers.TryGetValue(ApiKeyHeader, out var apiKey))
        {
            context.Response.StatusCode = 401;
            await context.Response.WriteAsync("API Key required");
            return;
        }
        // Validate API key (in production, check against database)
        var validApiKey = context.RequestServices
            .GetRequiredService<IConfiguration>()["ApiKey"];
        if (apiKey != validApiKey)
        {
            context.Response.StatusCode = 403;
            await context.Response.WriteAsync("Invalid API Key");
            return;
        }
        await _next(context);
    }
}
// In Program.cs
app.UseMiddleware<ApiKeyMiddleware>();
// Middleware/ApiKeyMiddleware.cs
public class ApiKeyMiddleware
{
    private readonly RequestDelegate _next;
    private const string ApiKeyHeader = "X-API-Key";
    public ApiKeyMiddleware(RequestDelegate next)
    {
        _next = next;
    }
    public async Task InvokeAsync(HttpContext context)
    {
        if (!context.Request.Headers.TryGetValue(ApiKeyHeader, out var apiKey))
        {
            context.Response.StatusCode = 401;
            await context.Response.WriteAsync("API Key required");
            return;
        }
        // Validate API key (in production, check against database)
        var validApiKey = context.RequestServices
            .GetRequiredService<IConfiguration>()["ApiKey"];
        if (apiKey != validApiKey)
        {
            context.Response.StatusCode = 403;
            await context.Response.WriteAsync("Invalid API Key");
            return;
        }
        await _next(context);
    }
}
// In Program.cs
app.UseMiddleware<ApiKeyMiddleware>();
Imports Microsoft.AspNetCore.Http
Imports Microsoft.Extensions.Configuration
Imports System.Threading.Tasks

' Middleware/ApiKeyMiddleware.vb
Public Class ApiKeyMiddleware
    Private ReadOnly _next As RequestDelegate
    Private Const ApiKeyHeader As String = "X-API-Key"

    Public Sub New(next As RequestDelegate)
        _next = next
    End Sub

    Public Async Function InvokeAsync(context As HttpContext) As Task
        Dim apiKey As String = Nothing
        If Not context.Request.Headers.TryGetValue(ApiKeyHeader, apiKey) Then
            context.Response.StatusCode = 401
            Await context.Response.WriteAsync("API Key required")
            Return
        End If

        ' Validate API key (in production, check against database)
        Dim validApiKey As String = context.RequestServices.GetRequiredService(Of IConfiguration)()("ApiKey")
        If apiKey <> validApiKey Then
            context.Response.StatusCode = 403
            Await context.Response.WriteAsync("Invalid API Key")
            Return
        End If

        Await _next(context)
    End Function
End Class

' In Program.vb
app.UseMiddleware(Of ApiKeyMiddleware)()
$vbLabelText   $csharpLabel

For more advanced authentication scenarios, consider:

Real-World Example: Invoice Generation API

Let's build a practical invoice generation endpoint that demonstrates a complete implementation. This example shows how a production .NET PDF API can generate professional invoices with dynamic data.

Get stated with IronPDF now.
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First, we'll create a new file in our Models folder. Here, I've called mine Invoice.cs. Then, add the following code to your new file.

public class Invoice
{
    public string InvoiceNumber { get; set; }
    public DateTime Date { get; set; }
    public string CustomerName { get; set; }
    public string CustomerAddress { get; set; }
    public List<InvoiceItem> Items { get; set; }
    public decimal Tax { get; set; }
}
public class InvoiceItem
{
    public string Description { get; set; }
    public int Quantity { get; set; }
    public decimal UnitPrice { get; set; }
    public decimal Total => Quantity * UnitPrice;
}
public class Invoice
{
    public string InvoiceNumber { get; set; }
    public DateTime Date { get; set; }
    public string CustomerName { get; set; }
    public string CustomerAddress { get; set; }
    public List<InvoiceItem> Items { get; set; }
    public decimal Tax { get; set; }
}
public class InvoiceItem
{
    public string Description { get; set; }
    public int Quantity { get; set; }
    public decimal UnitPrice { get; set; }
    public decimal Total => Quantity * UnitPrice;
}
Public Class Invoice
    Public Property InvoiceNumber As String
    Public Property [Date] As DateTime
    Public Property CustomerName As String
    Public Property CustomerAddress As String
    Public Property Items As List(Of InvoiceItem)
    Public Property Tax As Decimal
End Class

Public Class InvoiceItem
    Public Property Description As String
    Public Property Quantity As Integer
    Public Property UnitPrice As Decimal
    Public ReadOnly Property Total As Decimal
        Get
            Return Quantity * UnitPrice
        End Get
    End Property
End Class
$vbLabelText   $csharpLabel

Then, we'll need to create a new service file for our invoice generator. In your Services folder, add the following code. For mine, I made a new file called InvoiceService.cs. This code will handle the styling and layout of our Invoice PDF file.

public class InvoiceService
{
    private readonly ChromePdfRenderer _renderer;
    public InvoiceService()
    {
        _renderer = new ChromePdfRenderer();
        _renderer.RenderingOptions.MarginTop = 10;
        _renderer.RenderingOptions.MarginBottom = 10;
        _renderer.RenderingOptions.PrintHtmlBackgrounds = true;
    }
    public byte[] GenerateInvoice(Invoice invoice)
{
    var html = BuildInvoiceHtml(invoice);
    // Add footer with page numbers
    _renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
    {
        MaxHeight = 15,
        HtmlFragment = "<center><i>{page} of {total-pages}</i></center>",
        DrawDividerLine = true
    };
    var pdf = _renderer.RenderHtmlAsPdf(html);
    return pdf.BinaryData;
}
    private string BuildInvoiceHtml(Invoice invoice)
    {
        var subtotal = invoice.Items.Sum(i => i.Total);
        var taxAmount = subtotal * (invoice.Tax / 100);
        var total = subtotal + taxAmount;
        var itemsHtml = string.Join("", invoice.Items.Select(item => 
            $@"<tr>
                <td>{item.Description}</td>
                <td class='text-center'>{item.Quantity}</td>
                <td class='text-right'>${item.UnitPrice:F2}</td>
                <td class='text-right'>${item.Total:F2}</td>
            </tr>"));
        return $@"
        <!DOCTYPE html>
        <html>
        <head>
            <style>
                body {{ font-family: Arial, sans-serif; }}
                .invoice-header {{ 
                    background-color: #f8f9fa; 
                    padding: 20px; 
                    margin-bottom: 20px; 
                }}
                table {{ 
                    width: 100%; 
                    border-collapse: collapse; 
                }}
                th, td {{ 
                    padding: 10px; 
                    border-bottom: 1px solid #ddd; 
                }}
                th {{ 
                    background-color: #007bff; 
                    color: white; 
                }}
                .text-right {{ text-align: right; }}
                .text-center {{ text-align: center; }}
                .total-section {{ 
                    margin-top: 20px; 
                    text-align: right; 
                }}
            </style>
        </head>
        <body>
            <div class='invoice-header'>
                <h1>Invoice #{invoice.InvoiceNumber}</h1>
                <p>Date: {invoice.Date:yyyy-MM-dd}</p>
            </div>   
            <div>
                <h3>Bill To:</h3>
                <p>{invoice.CustomerName}<br/>{invoice.CustomerAddress}</p>
            </div>    
            <table>
                <thead>
                    <tr>
                        <th>Description</th>
                        <th>Quantity</th>
                        <th>Unit Price</th>
                        <th>Total</th>
                    </tr>
                </thead>
                <tbody>
                    {itemsHtml}
                </tbody>
            </table>
            <div class='total-section'>
                <p>Subtotal: ${subtotal:F2}</p>
                <p>Tax ({invoice.Tax}%): ${taxAmount:F2}</p>
                <h3>Total: ${total:F2}</h3>
            </div>
        </body>
        </html>";
    }
}
public class InvoiceService
{
    private readonly ChromePdfRenderer _renderer;
    public InvoiceService()
    {
        _renderer = new ChromePdfRenderer();
        _renderer.RenderingOptions.MarginTop = 10;
        _renderer.RenderingOptions.MarginBottom = 10;
        _renderer.RenderingOptions.PrintHtmlBackgrounds = true;
    }
    public byte[] GenerateInvoice(Invoice invoice)
{
    var html = BuildInvoiceHtml(invoice);
    // Add footer with page numbers
    _renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
    {
        MaxHeight = 15,
        HtmlFragment = "<center><i>{page} of {total-pages}</i></center>",
        DrawDividerLine = true
    };
    var pdf = _renderer.RenderHtmlAsPdf(html);
    return pdf.BinaryData;
}
    private string BuildInvoiceHtml(Invoice invoice)
    {
        var subtotal = invoice.Items.Sum(i => i.Total);
        var taxAmount = subtotal * (invoice.Tax / 100);
        var total = subtotal + taxAmount;
        var itemsHtml = string.Join("", invoice.Items.Select(item => 
            $@"<tr>
                <td>{item.Description}</td>
                <td class='text-center'>{item.Quantity}</td>
                <td class='text-right'>${item.UnitPrice:F2}</td>
                <td class='text-right'>${item.Total:F2}</td>
            </tr>"));
        return $@"
        <!DOCTYPE html>
        <html>
        <head>
            <style>
                body {{ font-family: Arial, sans-serif; }}
                .invoice-header {{ 
                    background-color: #f8f9fa; 
                    padding: 20px; 
                    margin-bottom: 20px; 
                }}
                table {{ 
                    width: 100%; 
                    border-collapse: collapse; 
                }}
                th, td {{ 
                    padding: 10px; 
                    border-bottom: 1px solid #ddd; 
                }}
                th {{ 
                    background-color: #007bff; 
                    color: white; 
                }}
                .text-right {{ text-align: right; }}
                .text-center {{ text-align: center; }}
                .total-section {{ 
                    margin-top: 20px; 
                    text-align: right; 
                }}
            </style>
        </head>
        <body>
            <div class='invoice-header'>
                <h1>Invoice #{invoice.InvoiceNumber}</h1>
                <p>Date: {invoice.Date:yyyy-MM-dd}</p>
            </div>   
            <div>
                <h3>Bill To:</h3>
                <p>{invoice.CustomerName}<br/>{invoice.CustomerAddress}</p>
            </div>    
            <table>
                <thead>
                    <tr>
                        <th>Description</th>
                        <th>Quantity</th>
                        <th>Unit Price</th>
                        <th>Total</th>
                    </tr>
                </thead>
                <tbody>
                    {itemsHtml}
                </tbody>
            </table>
            <div class='total-section'>
                <p>Subtotal: ${subtotal:F2}</p>
                <p>Tax ({invoice.Tax}%): ${taxAmount:F2}</p>
                <h3>Total: ${total:F2}</h3>
            </div>
        </body>
        </html>";
    }
}
Imports System
Imports System.Linq

Public Class InvoiceService
    Private ReadOnly _renderer As ChromePdfRenderer

    Public Sub New()
        _renderer = New ChromePdfRenderer()
        _renderer.RenderingOptions.MarginTop = 10
        _renderer.RenderingOptions.MarginBottom = 10
        _renderer.RenderingOptions.PrintHtmlBackgrounds = True
    End Sub

    Public Function GenerateInvoice(invoice As Invoice) As Byte()
        Dim html = BuildInvoiceHtml(invoice)
        ' Add footer with page numbers
        _renderer.RenderingOptions.HtmlFooter = New HtmlHeaderFooter With {
            .MaxHeight = 15,
            .HtmlFragment = "<center><i>{page} of {total-pages}</i></center>",
            .DrawDividerLine = True
        }
        Dim pdf = _renderer.RenderHtmlAsPdf(html)
        Return pdf.BinaryData
    End Function

    Private Function BuildInvoiceHtml(invoice As Invoice) As String
        Dim subtotal = invoice.Items.Sum(Function(i) i.Total)
        Dim taxAmount = subtotal * (invoice.Tax / 100)
        Dim total = subtotal + taxAmount
        Dim itemsHtml = String.Join("", invoice.Items.Select(Function(item) 
            $"<tr>
                <td>{item.Description}</td>
                <td class='text-center'>{item.Quantity}</td>
                <td class='text-right'>${item.UnitPrice:F2}</td>
                <td class='text-right'>${item.Total:F2}</td>
            </tr>"))
        Return $"
        <!DOCTYPE html>
        <html>
        <head>
            <style>
                body {{ font-family: Arial, sans-serif; }}
                .invoice-header {{ 
                    background-color: #f8f9fa; 
                    padding: 20px; 
                    margin-bottom: 20px; 
                }}
                table {{ 
                    width: 100%; 
                    border-collapse: collapse; 
                }}
                th, td {{ 
                    padding: 10px; 
                    border-bottom: 1px solid #ddd; 
                }}
                th {{ 
                    background-color: #007bff; 
                    color: white; 
                }}
                .text-right {{ text-align: right; }}
                .text-center {{ text-align: center; }}
                .total-section {{ 
                    margin-top: 20px; 
                    text-align: right; 
                }}
            </style>
        </head>
        <body>
            <div class='invoice-header'>
                <h1>Invoice #{invoice.InvoiceNumber}</h1>
                <p>Date: {invoice.Date:yyyy-MM-dd}</p>
            </div>   
            <div>
                <h3>Bill To:</h3>
                <p>{invoice.CustomerName}<br/>{invoice.CustomerAddress}</p>
            </div>    
            <table>
                <thead>
                    <tr>
                        <th>Description</th>
                        <th>Quantity</th>
                        <th>Unit Price</th>
                        <th>Total</th>
                    </tr>
                </thead>
                <tbody>
                    {itemsHtml}
                </tbody>
            </table>
            <div class='total-section'>
                <p>Subtotal: ${subtotal:F2}</p>
                <p>Tax ({invoice.Tax}%): ${taxAmount:F2}</p>
                <h3>Total: ${total:F2}</h3>
            </div>
        </body>
        </html>"
    End Function
End Class
$vbLabelText   $csharpLabel

Finally, you will need to create a new Controller in order to access and create a new Invoice using the API.

[ApiController]
[Route("api/[controller]")]
public class InvoiceController : ControllerBase
{
    private readonly InvoiceService _invoiceService;
    public InvoiceController(InvoiceService invoiceService)
    {
        _invoiceService = invoiceService;
    }
    [HttpPost("generate")]
    public IActionResult GenerateInvoice([FromBody] Invoice invoice)
    {
        try
        {
            var pdfBytes = _invoiceService.GenerateInvoice(invoice);
            var fileName = $"Invoice_{invoice.InvoiceNumber}.pdf";
            return File(pdfBytes, "application/pdf", fileName);
        }
        catch (Exception ex)
        {
            return StatusCode(500, $"Error generating invoice: {ex.Message}");
        }
    }
}
[ApiController]
[Route("api/[controller]")]
public class InvoiceController : ControllerBase
{
    private readonly InvoiceService _invoiceService;
    public InvoiceController(InvoiceService invoiceService)
    {
        _invoiceService = invoiceService;
    }
    [HttpPost("generate")]
    public IActionResult GenerateInvoice([FromBody] Invoice invoice)
    {
        try
        {
            var pdfBytes = _invoiceService.GenerateInvoice(invoice);
            var fileName = $"Invoice_{invoice.InvoiceNumber}.pdf";
            return File(pdfBytes, "application/pdf", fileName);
        }
        catch (Exception ex)
        {
            return StatusCode(500, $"Error generating invoice: {ex.Message}");
        }
    }
}
Imports Microsoft.AspNetCore.Mvc

<ApiController>
<Route("api/[controller]")>
Public Class InvoiceController
    Inherits ControllerBase

    Private ReadOnly _invoiceService As InvoiceService

    Public Sub New(invoiceService As InvoiceService)
        _invoiceService = invoiceService
    End Sub

    <HttpPost("generate")>
    Public Function GenerateInvoice(<FromBody> invoice As Invoice) As IActionResult
        Try
            Dim pdfBytes = _invoiceService.GenerateInvoice(invoice)
            Dim fileName = $"Invoice_{invoice.InvoiceNumber}.pdf"
            Return File(pdfBytes, "application/pdf", fileName)
        Catch ex As Exception
            Return StatusCode(500, $"Error generating invoice: {ex.Message}")
        End Try
    End Function
End Class
$vbLabelText   $csharpLabel

Invoice Output

How to create .NET PDF API Using IronPDF: Figure 7 - PDF Invoice output

Container Deployment Considerations

While this tutorial focuses on local development, here's a brief overview of containerizing your PDF API:

Basic Dockerfile

FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
WORKDIR /app
EXPOSE 80
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ["PdfApiService.csproj", "."]
RUN dotnet restore
COPY . .
RUN dotnet build -c Release -o /app/build
FROM build AS publish
RUN dotnet publish -c Release -o /app/publish
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
# IronPDF requires additional dependencies on Linux
RUN apt-get update && apt-get install -y \
    libgdiplus \
    libc6-dev \
    libx11-dev \
    && rm -rf /var/lib/apt/lists/*     
ENTRYPOINT ["dotnet", "PdfApiService.dll"]
FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
WORKDIR /app
EXPOSE 80
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ["PdfApiService.csproj", "."]
RUN dotnet restore
COPY . .
RUN dotnet build -c Release -o /app/build
FROM build AS publish
RUN dotnet publish -c Release -o /app/publish
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
# IronPDF requires additional dependencies on Linux
RUN apt-get update && apt-get install -y \
    libgdiplus \
    libc6-dev \
    libx11-dev \
    && rm -rf /var/lib/apt/lists/*     
ENTRYPOINT ["dotnet", "PdfApiService.dll"]
The provided code is a Dockerfile written for building and running a .NET application, not C# code. Dockerfiles are not converted to VB.NET as they are not programming language code but configuration scripts for Docker. If you have C# code that needs conversion to VB.NET, please provide that code instead.
$vbLabelText   $csharpLabel

For detailed deployment guides for your .NET PDF API, see:

Error Handling Best Practices

For a more fault-tolerant program, the best practices are to implement a global error handler for consistent error responses, such as below:

// Middleware/ErrorHandlingMiddleware.cs
public class ErrorHandlingMiddleware
{
    private readonly RequestDelegate _next;
    public ErrorHandlingMiddleware(RequestDelegate next)
    {
        _next = next;
    }
    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await _next(context);
        }
        catch (Exception ex)
        {
            await HandleExceptionAsync(context, ex);
        }
    }
    private static async Task HandleExceptionAsync(HttpContext context, Exception ex)
    {
        context.Response.ContentType = "application/json";
        context.Response.StatusCode = 500;
        var response = new
        {
            error = "An error occurred processing your request",
            message = ex.Message
        };
        await context.Response.WriteAsync(JsonSerializer.Serialize(response));
    }
}
// Middleware/ErrorHandlingMiddleware.cs
public class ErrorHandlingMiddleware
{
    private readonly RequestDelegate _next;
    public ErrorHandlingMiddleware(RequestDelegate next)
    {
        _next = next;
    }
    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await _next(context);
        }
        catch (Exception ex)
        {
            await HandleExceptionAsync(context, ex);
        }
    }
    private static async Task HandleExceptionAsync(HttpContext context, Exception ex)
    {
        context.Response.ContentType = "application/json";
        context.Response.StatusCode = 500;
        var response = new
        {
            error = "An error occurred processing your request",
            message = ex.Message
        };
        await context.Response.WriteAsync(JsonSerializer.Serialize(response));
    }
}
Imports System.Text.Json
Imports Microsoft.AspNetCore.Http
Imports System.Threading.Tasks

Public Class ErrorHandlingMiddleware
    Private ReadOnly _next As RequestDelegate

    Public Sub New(next As RequestDelegate)
        _next = next
    End Sub

    Public Async Function InvokeAsync(context As HttpContext) As Task
        Try
            Await _next(context)
        Catch ex As Exception
            Await HandleExceptionAsync(context, ex)
        End Try
    End Function

    Private Shared Async Function HandleExceptionAsync(context As HttpContext, ex As Exception) As Task
        context.Response.ContentType = "application/json"
        context.Response.StatusCode = 500
        Dim response = New With {
            .error = "An error occurred processing your request",
            .message = ex.Message
        }
        Await context.Response.WriteAsync(JsonSerializer.Serialize(response))
    End Function
End Class
$vbLabelText   $csharpLabel

For specific IronPDF troubleshooting scenarios, refer to the IronPDF troubleshooting guide.

Conclusion

You've now built a robust .NET PDF API using ASP.NET Core and IronPDF that can handle various document generation scenarios. This REST API provides a solid foundation for centralized PDF operations in your applications.

Key takeaways:

  • IronPDF makes PDF generation in Web API projects straightforward with its Chrome-based rendering
  • You can easily adjust your Web API to edit existing PDF documents with IronPDF's advanced editing tools
  • RESTful design principles ensure your PDF API is intuitive and maintainable
  • Proper error handling and security measures are essential for production
  • Performance optimization through async operations and caching improves scalability
  • You will have support for desktop and web applications with scalable document solutions

IronPDF allows developers to create PDF documents, save PDF files, and convert HTML efficiently, making it the essential PDF document API for modern .NET Framework applications.

Next Steps

Ready to implement IronPDF in your production .NET PDF API? Here are your next actions:

  1. Start your free trial - Test IronPDF with full functionality in your development environment
  2. Explore advanced features - Check out digital signatures, PDF forms, and other advanced PDF features
  3. Scale with confidence - Review licensing options for your production API needs

Build your .NET PDF API today and streamline document generation across your entire application ecosystem with IronPDF!

Frequently Asked Questions

What is a .NET PDF API?

A .NET PDF API is a library that allows developers to create, edit, and extract PDF content within .NET applications. It simplifies complex PDF tasks and ensures efficient management of PDF files.

How can a .NET PDF API benefit my application?

A .NET PDF API can enhance your application by providing consistency, maintainability, and scalability in managing PDF files, such as generating invoices, reports, certificates, or contracts.

What are some common use cases for a .NET PDF API?

Common use cases for a .NET PDF API include generating invoices, creating reports, producing certificates, and managing contracts within desktop and web applications.

How does IronPDF simplify PDF generation tasks?

IronPDF simplifies PDF generation tasks by offering a robust library that allows for easy management of document content, PDF pages, and form fields, making it easier to maintain and scale applications.

Can IronPDF handle PDF form fields?

Yes, IronPDF can efficiently manage PDF form fields, allowing developers to create, fill, and extract data from forms within PDF documents.

Is IronPDF suitable for both desktop and web applications?

Absolutely, IronPDF is designed to work seamlessly across both desktop and web applications, providing a consistent and scalable solution for PDF management.

What makes IronPDF a reliable choice for .NET developers?

IronPDF is a reliable choice for .NET developers due to its ease of use, comprehensive features, and ability to streamline PDF tasks, which enhances productivity and application performance.

Does IronPDF support PDF extraction capabilities?

Yes, IronPDF supports PDF extraction capabilities, allowing you to extract text, images, and other data from PDF documents efficiently.

How does IronPDF improve scalability in managing PDFs?

IronPDF improves scalability by providing a centralized PDF generation service that can handle increasing demands without sacrificing performance, making it ideal for growing applications.

What kind of support does IronPDF offer for .NET applications?

IronPDF offers extensive support for .NET applications, including detailed documentation, sample code, and a responsive support team to assist developers in integrating PDF functionalities.

Is IronPDF fully compatible with .NET 10?

Yes — IronPDF is fully compatible with .NET 10. It supports all the performance, language, and runtime enhancements that .NET 10 introduces, and works out-of-the-box in .NET 10 projects just as it has with past versions such as .NET 6, 7, 8, and 9.

Curtis Chau
Curtis Chau
  Chat with engineering team now
Technical Writer

Curtis Chau holds a Bachelor’s degree in Computer Science (Carleton University) and specializes in front-end development with expertise in Node.js, TypeScript, JavaScript, and React. Passionate about crafting intuitive and aesthetically pleasing user interfaces, Curtis enjoys working with modern frameworks and creating well-structured, visually appealing manuals.

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