MIGRATION GUIDES

How to Migrate from Aspose.PDF to IronPDF in C#

Published:January 11, 2026

Why Migrate Away from Aspose.PDF?

While Aspose.PDF delivers enterprise-grade functionality, several factors drive development teams to seek modern alternatives for their PDF generation needs.

Cost Comparison

Aspose.PDF uses a traditional enterprise licensing model with annual renewals that accumulate significantly over time:

Aspect	Aspose.PDF	IronPDF
Starting Price	$1,199/developer/year	$749 one-time (Lite)
License Model	Annual subscription + renewal	Perpetual license
OEM License	$5,997+ additional	Included in higher tiers
Support	Extra cost tiers	Included
Total 3-Year Cost	$3,597+ per developer	$749 one-time

HTML Rendering Engine Comparison

Aspose.PDF uses the Flying Saucer CSS engine, which struggles with modern web standards. IronPDF leverages a full Chromium rendering engine:

Feature	Aspose.PDF (Flying Saucer)	IronPDF (Chromium)
CSS3 Support	Limited (older CSS)	Full CSS3
Flexbox/Grid	Not supported	Full support
JavaScript	Very limited	Full support
Web Fonts	Partial	Complete
Modern HTML5	Limited	Complete
Rendering Quality	Variable	Pixel-perfect

Documented Performance Issues

Users have reported significant performance differences between the two libraries:

Metric	Aspose.PDF	IronPDF
HTML Rendering	Documented slowdowns (30x slower in some cases)	Optimized Chromium engine
Large Documents	Memory issues reported	Efficient streaming
Linux Performance	High CPU, memory leaks reported	Stable

Aspose.PDF vs. IronPDF: Key Differences

Aspect	Aspose.PDF	IronPDF
Pricing	$1,199/developer/year (subscription)	$749 one-time (Lite)
HTML Engine	Flying Saucer (limited CSS)	Chromium (full CSS3/JS)
Performance	Documented slowdowns	Optimized
License Model	Annual renewal + .lic file	Perpetual + code-based key
Linux Support	Issues reported (CPU, memory)	Stable
Page Indexing	1-based (`Pages[1]`)	0-based (`Pages[0]`)

Pre-Migration Preparation

Prerequisites

Ensure your environment meets these requirements:

.NET Framework 4.6.2+ or .NET Core 3.1 / .NET 5-9
Visual Studio 2019+ or VS Code with C# extension
NuGet Package Manager access
IronPDF license key (free trial available at ironpdf.com)

Audit Aspose.PDF Usage

Run these commands in your solution directory to identify all Aspose.PDF references:

# Find all Aspose.Pdf using statements
grep -r "using Aspose.Pdf" --include="*.cs" .

# Find HtmlLoadOptions usage
grep -r "HtmlLoadOptions\|HtmlFragment" --include="*.cs" .

# Find Facades usage
grep -r "PdfFileEditor\|PdfFileMend\|PdfFileStamp" --include="*.cs" .

# Find TextAbsorber usage
grep -r "TextAbsorber\|TextFragmentAbsorber" --include="*.cs" .

# Find all Aspose.Pdf using statements
grep -r "using Aspose.Pdf" --include="*.cs" .

# Find HtmlLoadOptions usage
grep -r "HtmlLoadOptions\|HtmlFragment" --include="*.cs" .

# Find Facades usage
grep -r "PdfFileEditor\|PdfFileMend\|PdfFileStamp" --include="*.cs" .

# Find TextAbsorber usage
grep -r "TextAbsorber\|TextFragmentAbsorber" --include="*.cs" .

SHELL

Breaking Changes to Anticipate

Aspose.PDF Pattern	Change Required
`new Document()` + `Pages.Add()`	Use HTML rendering instead
`HtmlLoadOptions`	`ChromePdfRenderer.RenderHtmlAsPdf()`
`TextFragment` + manual positioning	CSS-based positioning
`PdfFileEditor.Concatenate()`	`PdfDocument.Merge()`
`TextFragmentAbsorber`	`pdf.ExtractAllText()`
`ImageStamp`	HTML-based watermarks
`.lic` file licensing	Code-based license key
1-based page indexing	0-based page indexing

Step-by-Step Migration Process

Step 1: Update NuGet Packages

Remove Aspose.PDF and install IronPDF:

# Remove Aspose.PDF
dotnet remove package Aspose.PDF

# Install IronPDF
dotnet add package IronPdf

# Remove Aspose.PDF
dotnet remove package Aspose.PDF

# Install IronPDF
dotnet add package IronPdf

SHELL

Or via Package Manager Console:

Uninstall-Package Aspose.PDF
Install-Package IronPdf

Step 2: Update Namespace References

Replace Aspose.PDF namespaces with IronPDF:

// Remove these
using Aspose.Pdf;
using Aspose.Pdf.Text;
using Aspose.Pdf.Facades;
using Aspose.Pdf.Generator;

// Add these
using IronPdf;
using IronPdf.Rendering;
using IronPdf.Editing;

// Remove these
using Aspose.Pdf;
using Aspose.Pdf.Text;
using Aspose.Pdf.Facades;
using Aspose.Pdf.Generator;

// Add these
using IronPdf;
using IronPdf.Rendering;
using IronPdf.Editing;

$vbLabelText $csharpLabel

Step 3: Update License Configuration

Aspose.PDF uses .lic file licensing. IronPDF uses a simple code-based key.

Aspose.PDF Implementation:

var license = new Aspose.Pdf.License();
license.SetLicense("Aspose.Pdf.lic");

var license = new Aspose.Pdf.License();
license.SetLicense("Aspose.Pdf.lic");

$vbLabelText $csharpLabel

IronPDF Implementation:

IronPdf.License.LicenseKey = "YOUR-IRONPDF-LICENSE-KEY";

IronPdf.License.LicenseKey = "YOUR-IRONPDF-LICENSE-KEY";

$vbLabelText $csharpLabel

Complete API Migration Reference

Core Class Mapping

Aspose.PDF Class	IronPDF Equivalent	Notes
`Document`	`PdfDocument`	Main document class
`HtmlLoadOptions`	`ChromePdfRenderer`	HTML to PDF
`TextFragmentAbsorber`	`PdfDocument.ExtractAllText()`	Text extraction
`PdfFileEditor`	`PdfDocument.Merge()`	Merge/split operations
`TextStamp` / `ImageStamp`	`PdfDocument.ApplyWatermark()`	Watermarks
`License`	`IronPdf.License`	Licensing

Document Operations

Aspose.PDF Method	IronPDF Method	Notes
`new Document()`	`new PdfDocument()`	Empty document
`new Document(path)`	`PdfDocument.FromFile(path)`	Load from file
`doc.Save(path)`	`pdf.SaveAs(path)`	Save to file
`doc.Pages.Count`	`pdf.PageCount`	Page count
`doc.Pages.Delete(index)`	`pdf.RemovePage(index)`	Remove page

HTML to PDF Conversion

Aspose.PDF Method	IronPDF Method	Notes
`new HtmlLoadOptions()`	`new ChromePdfRenderer()`	HTML renderer
`new Document(stream, htmlOptions)`	`renderer.RenderHtmlAsPdf(html)`	HTML string
`new Document(path, htmlOptions)`	`renderer.RenderHtmlFileAsPdf(path)`	HTML file

Code Migration Examples

HTML String to PDF

The most common Aspose.PDF operation demonstrates the fundamental difference in approach—Aspose.PDF requires wrapping HTML in a MemoryStream, while IronPDF accepts strings directly.

Aspose.PDF Implementation:

// NuGet: Install-Package Aspose.PDF
using Aspose.Pdf;
using System;
using System.IO;
using System.Text;

class Program
{
    static void Main()
    {
        string htmlContent = "<html><body><h1>Hello World</h1><p>This is a PDF from HTML string.</p></body></html>";

        using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(htmlContent)))
        {
            var htmlLoadOptions = new HtmlLoadOptions();
            var document = new Document(stream, htmlLoadOptions);
            document.Save("output.pdf");
        }

        Console.WriteLine("PDF created from HTML string");
    }
}

// NuGet: Install-Package Aspose.PDF
using Aspose.Pdf;
using System;
using System.IO;
using System.Text;

class Program
{
    static void Main()
    {
        string htmlContent = "<html><body><h1>Hello World</h1><p>This is a PDF from HTML string.</p></body></html>";

        using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(htmlContent)))
        {
            var htmlLoadOptions = new HtmlLoadOptions();
            var document = new Document(stream, htmlLoadOptions);
            document.Save("output.pdf");
        }

        Console.WriteLine("PDF created from HTML string");
    }
}

$vbLabelText $csharpLabel

IronPDF Implementation:

// NuGet: Install-Package IronPdf
using IronPdf;
using System;

class Program
{
    static void Main()
    {
        string htmlContent = "<html><body><h1>Hello World</h1><p>This is a PDF from HTML string.</p></body></html>";

        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf(htmlContent);
        pdf.SaveAs("output.pdf");

        Console.WriteLine("PDF created from HTML string");
    }
}

// NuGet: Install-Package IronPdf
using IronPdf;
using System;

class Program
{
    static void Main()
    {
        string htmlContent = "<html><body><h1>Hello World</h1><p>This is a PDF from HTML string.</p></body></html>";

        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf(htmlContent);
        pdf.SaveAs("output.pdf");

        Console.WriteLine("PDF created from HTML string");
    }
}

$vbLabelText $csharpLabel

IronPDF eliminates the MemoryStream wrapper entirely—a cleaner, more intuitive API.

HTML File to PDF

Aspose.PDF Implementation:

// NuGet: Install-Package Aspose.PDF
using Aspose.Pdf;
using System;

class Program
{
    static void Main()
    {
        var htmlLoadOptions = new HtmlLoadOptions();
        var document = new Document("input.html", htmlLoadOptions);
        document.Save("output.pdf");
        Console.WriteLine("PDF created successfully");
    }
}

// NuGet: Install-Package Aspose.PDF
using Aspose.Pdf;
using System;

class Program
{
    static void Main()
    {
        var htmlLoadOptions = new HtmlLoadOptions();
        var document = new Document("input.html", htmlLoadOptions);
        document.Save("output.pdf");
        Console.WriteLine("PDF created successfully");
    }
}

$vbLabelText $csharpLabel

IronPDF Implementation:

// NuGet: Install-Package IronPdf
using IronPdf;
using System;

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlFileAsPdf("input.html");
        pdf.SaveAs("output.pdf");
        Console.WriteLine("PDF created successfully");
    }
}

// NuGet: Install-Package IronPdf
using IronPdf;
using System;

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlFileAsPdf("input.html");
        pdf.SaveAs("output.pdf");
        Console.WriteLine("PDF created successfully");
    }
}

$vbLabelText $csharpLabel

Merging Multiple PDFs

Aspose.PDF requires iterating through pages manually. IronPDF provides a static Merge method.

Aspose.PDF Implementation:

// NuGet: Install-Package Aspose.PDF
using Aspose.Pdf;
using System;

class Program
{
    static void Main()
    {
        var document1 = new Document("file1.pdf");
        var document2 = new Document("file2.pdf");

        foreach (Page page in document2.Pages)
        {
            document1.Pages.Add(page);
        }

        document1.Save("merged.pdf");
        Console.WriteLine("PDFs merged successfully");
    }
}

// NuGet: Install-Package Aspose.PDF
using Aspose.Pdf;
using System;

class Program
{
    static void Main()
    {
        var document1 = new Document("file1.pdf");
        var document2 = new Document("file2.pdf");

        foreach (Page page in document2.Pages)
        {
            document1.Pages.Add(page);
        }

        document1.Save("merged.pdf");
        Console.WriteLine("PDFs merged successfully");
    }
}

$vbLabelText $csharpLabel

IronPDF Implementation:

// NuGet: Install-Package IronPdf
using IronPdf;
using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var pdf1 = PdfDocument.FromFile("file1.pdf");
        var pdf2 = PdfDocument.FromFile("file2.pdf");

        var merged = PdfDocument.Merge(pdf1, pdf2);
        merged.SaveAs("merged.pdf");

        Console.WriteLine("PDFs merged successfully");
    }
}

// NuGet: Install-Package IronPdf
using IronPdf;
using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var pdf1 = PdfDocument.FromFile("file1.pdf");
        var pdf2 = PdfDocument.FromFile("file2.pdf");

        var merged = PdfDocument.Merge(pdf1, pdf2);
        merged.SaveAs("merged.pdf");

        Console.WriteLine("PDFs merged successfully");
    }
}

$vbLabelText $csharpLabel

Text Extraction

Aspose.PDF Implementation:

using Aspose.Pdf;
using Aspose.Pdf.Text;

var document = new Document("document.pdf");
var absorber = new TextAbsorber();

foreach (Page page in document.Pages)
{
    page.Accept(absorber);
}

string extractedText = absorber.Text;
Console.WriteLine(extractedText);

using Aspose.Pdf;
using Aspose.Pdf.Text;

var document = new Document("document.pdf");
var absorber = new TextAbsorber();

foreach (Page page in document.Pages)
{
    page.Accept(absorber);
}

string extractedText = absorber.Text;
Console.WriteLine(extractedText);

$vbLabelText $csharpLabel

IronPDF Implementation:

using IronPdf;

var pdf = PdfDocument.FromFile("document.pdf");

// Extract all text - one line!
string allText = pdf.ExtractAllText();
Console.WriteLine(allText);

// Or extract from specific page
string page1Text = pdf.ExtractTextFromPage(0);

using IronPdf;

var pdf = PdfDocument.FromFile("document.pdf");

// Extract all text - one line!
string allText = pdf.ExtractAllText();
Console.WriteLine(allText);

// Or extract from specific page
string page1Text = pdf.ExtractTextFromPage(0);

$vbLabelText $csharpLabel

IronPDF simplifies text extraction from multiple steps to a single method call.

Adding Watermarks

Aspose.PDF Implementation:

using Aspose.Pdf;
using Aspose.Pdf.Text;

var document = new Document("document.pdf");

var textStamp = new TextStamp("CONFIDENTIAL");
textStamp.Background = true;
textStamp.XIndent = 100;
textStamp.YIndent = 100;
textStamp.Rotate = Rotation.on45;
textStamp.Opacity = 0.5;
textStamp.TextState.Font = FontRepository.FindFont("Arial");
textStamp.TextState.FontSize = 72;
textStamp.TextState.ForegroundColor = Color.Red;

foreach (Page page in document.Pages)
{
    page.AddStamp(textStamp);
}

document.Save("watermarked.pdf");

using Aspose.Pdf;
using Aspose.Pdf.Text;

var document = new Document("document.pdf");

var textStamp = new TextStamp("CONFIDENTIAL");
textStamp.Background = true;
textStamp.XIndent = 100;
textStamp.YIndent = 100;
textStamp.Rotate = Rotation.on45;
textStamp.Opacity = 0.5;
textStamp.TextState.Font = FontRepository.FindFont("Arial");
textStamp.TextState.FontSize = 72;
textStamp.TextState.ForegroundColor = Color.Red;

foreach (Page page in document.Pages)
{
    page.AddStamp(textStamp);
}

document.Save("watermarked.pdf");

$vbLabelText $csharpLabel

IronPDF Implementation:

using IronPdf;
using IronPdf.Editing;

var pdf = PdfDocument.FromFile("document.pdf");

// HTML-based watermark with full styling control
string watermarkHtml = @"
<div style='
    color: red;
    opacity: 0.5;
    font-family: Arial;
    font-size: 72px;
    font-weight: bold;
    text-align: center;
'>CONFIDENTIAL</div>";

pdf.ApplyWatermark(watermarkHtml,
    rotation: 45,
    verticalAlignment: VerticalAlignment.Middle,
    horizontalAlignment: HorizontalAlignment.Center);

pdf.SaveAs("watermarked.pdf");

using IronPdf;
using IronPdf.Editing;

var pdf = PdfDocument.FromFile("document.pdf");

// HTML-based watermark with full styling control
string watermarkHtml = @"
<div style='
    color: red;
    opacity: 0.5;
    font-family: Arial;
    font-size: 72px;
    font-weight: bold;
    text-align: center;
'>CONFIDENTIAL</div>";

pdf.ApplyWatermark(watermarkHtml,
    rotation: 45,
    verticalAlignment: VerticalAlignment.Middle,
    horizontalAlignment: HorizontalAlignment.Center);

pdf.SaveAs("watermarked.pdf");

$vbLabelText $csharpLabel

IronPDF uses HTML/CSS-based watermarking, providing full styling control through familiar web technologies.

Password Protection

Aspose.PDF Implementation:

using Aspose.Pdf;

var document = new Document("document.pdf");
document.Encrypt("userPassword", "ownerPassword", DocumentPrivilege.ForbidAll, CryptoAlgorithm.AESx256);
document.Save("protected.pdf");

using Aspose.Pdf;

var document = new Document("document.pdf");
document.Encrypt("userPassword", "ownerPassword", DocumentPrivilege.ForbidAll, CryptoAlgorithm.AESx256);
document.Save("protected.pdf");

$vbLabelText $csharpLabel

IronPDF Implementation:

using IronPdf;

var pdf = PdfDocument.FromFile("document.pdf");

// Set passwords
pdf.SecuritySettings.UserPassword = "userPassword";
pdf.SecuritySettings.OwnerPassword = "ownerPassword";

// Set permissions
pdf.SecuritySettings.AllowUserPrinting = PdfPrintSecurity.FullPrintRights;
pdf.SecuritySettings.AllowUserCopyPasteContent = false;
pdf.SecuritySettings.AllowUserEdits = PdfEditSecurity.NoEdit;

pdf.SaveAs("protected.pdf");

using IronPdf;

var pdf = PdfDocument.FromFile("document.pdf");

// Set passwords
pdf.SecuritySettings.UserPassword = "userPassword";
pdf.SecuritySettings.OwnerPassword = "ownerPassword";

// Set permissions
pdf.SecuritySettings.AllowUserPrinting = PdfPrintSecurity.FullPrintRights;
pdf.SecuritySettings.AllowUserCopyPasteContent = false;
pdf.SecuritySettings.AllowUserEdits = PdfEditSecurity.NoEdit;

pdf.SaveAs("protected.pdf");

$vbLabelText $csharpLabel

IronPDF provides granular control over permissions through strongly-typed properties. For more options, see the encryption documentation.

Headers and Footers

IronPDF Implementation:

using IronPdf;

var renderer = new ChromePdfRenderer();

renderer.RenderingOptions.HtmlHeader = new HtmlHeaderFooter
{
    HtmlFragment = @"
        <div style='text-align:center; font-family:Arial; font-size:12px;'>
            Company Header
        </div>",
    DrawDividerLine = true,
    MaxHeight = 30
};

renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
{
    HtmlFragment = @"
        <div style='text-align:center; font-family:Arial; font-size:10px;'>
            Page {page} of {total-pages}
        </div>",
    DrawDividerLine = true,
    MaxHeight = 25
};

var pdf = renderer.RenderHtmlAsPdf("<h1>Content here</h1>");
pdf.SaveAs("with_headers.pdf");

using IronPdf;

var renderer = new ChromePdfRenderer();

renderer.RenderingOptions.HtmlHeader = new HtmlHeaderFooter
{
    HtmlFragment = @"
        <div style='text-align:center; font-family:Arial; font-size:12px;'>
            Company Header
        </div>",
    DrawDividerLine = true,
    MaxHeight = 30
};

renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
{
    HtmlFragment = @"
        <div style='text-align:center; font-family:Arial; font-size:10px;'>
            Page {page} of {total-pages}
        </div>",
    DrawDividerLine = true,
    MaxHeight = 25
};

var pdf = renderer.RenderHtmlAsPdf("<h1>Content here</h1>");
pdf.SaveAs("with_headers.pdf");

$vbLabelText $csharpLabel

IronPDF supports placeholder tokens like {page} and {total-pages} for dynamic page numbering. For more options, see the headers and footers documentation.

Critical Migration Notes

Page Indexing Change

Aspose.PDF uses 1-based indexing. IronPDF uses 0-based indexing:

// Aspose.PDF - 1-based indexing
var firstPage = doc.Pages[1];  // First page
var thirdPage = doc.Pages[3];  // Third page

// IronPDF - 0-based indexing
var firstPage = pdf.Pages[0];  // First page
var thirdPage = pdf.Pages[2];  // Third page

// Aspose.PDF - 1-based indexing
var firstPage = doc.Pages[1];  // First page
var thirdPage = doc.Pages[3];  // Third page

// IronPDF - 0-based indexing
var firstPage = pdf.Pages[0];  // First page
var thirdPage = pdf.Pages[2];  // Third page

$vbLabelText $csharpLabel

License File to Code Key

Replace .lic file licensing with code-based activation:

// Aspose.PDF
var license = new Aspose.Pdf.License();
license.SetLicense("Aspose.Pdf.lic");

// IronPDF
IronPdf.License.LicenseKey = "YOUR-LICENSE-KEY";
// Or from environment variable
IronPdf.License.LicenseKey = Environment.GetEnvironmentVariable("IRONPDF_LICENSE_KEY");

// Aspose.PDF
var license = new Aspose.Pdf.License();
license.SetLicense("Aspose.Pdf.lic");

// IronPDF
IronPdf.License.LicenseKey = "YOUR-LICENSE-KEY";
// Or from environment variable
IronPdf.License.LicenseKey = Environment.GetEnvironmentVariable("IRONPDF_LICENSE_KEY");

$vbLabelText $csharpLabel

ASP.NET Core Integration

IronPDF Pattern:

[ApiController]
[Route("[controller]")]
public class PdfController : ControllerBase
{
    [HttpGet("generate")]
    public IActionResult GeneratePdf()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf("<h1>Report</h1>");

        return File(pdf.BinaryData, "application/pdf", "report.pdf");
    }

    [HttpGet("generate-async")]
    public async Task<IActionResult> GeneratePdfAsync()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = await renderer.RenderHtmlAsPdfAsync("<h1>Report</h1>");

        return File(pdf.Stream, "application/pdf", "report.pdf");
    }
}

[ApiController]
[Route("[controller]")]
public class PdfController : ControllerBase
{
    [HttpGet("generate")]
    public IActionResult GeneratePdf()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf("<h1>Report</h1>");

        return File(pdf.BinaryData, "application/pdf", "report.pdf");
    }

    [HttpGet("generate-async")]
    public async Task<IActionResult> GeneratePdfAsync()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = await renderer.RenderHtmlAsPdfAsync("<h1>Report</h1>");

        return File(pdf.Stream, "application/pdf", "report.pdf");
    }
}

$vbLabelText $csharpLabel

Dependency Injection Configuration

// Program.cs
public void ConfigureServices(IServiceCollection services)
{
    // Set license once
    IronPdf.License.LicenseKey = Configuration["IronPdf:LicenseKey"];

    // Register renderer as scoped service
    services.AddScoped<ChromePdfRenderer>();
}

// Program.cs
public void ConfigureServices(IServiceCollection services)
{
    // Set license once
    IronPdf.License.LicenseKey = Configuration["IronPdf:LicenseKey"];

    // Register renderer as scoped service
    services.AddScoped<ChromePdfRenderer>();
}

$vbLabelText $csharpLabel

Performance Optimization

// 1. Reuse renderer instance
private static readonly ChromePdfRenderer SharedRenderer = new ChromePdfRenderer();

// 2. Disable unnecessary features for speed
var renderer = new ChromePdfRenderer();
renderer.RenderingOptions.EnableJavaScript = false; // If not needed
renderer.RenderingOptions.WaitFor.RenderDelay(0);   // No delay
renderer.RenderingOptions.Timeout = 30000;          // 30s max

// 3. Proper disposal
using (var pdf = renderer.RenderHtmlAsPdf(html))
{
    pdf.SaveAs("output.pdf");
}

// 1. Reuse renderer instance
private static readonly ChromePdfRenderer SharedRenderer = new ChromePdfRenderer();

// 2. Disable unnecessary features for speed
var renderer = new ChromePdfRenderer();
renderer.RenderingOptions.EnableJavaScript = false; // If not needed
renderer.RenderingOptions.WaitFor.RenderDelay(0);   // No delay
renderer.RenderingOptions.Timeout = 30000;          // 30s max

// 3. Proper disposal
using (var pdf = renderer.RenderHtmlAsPdf(html))
{
    pdf.SaveAs("output.pdf");
}

$vbLabelText $csharpLabel

Troubleshooting Common Migration Issues

Issue: HtmlLoadOptions Not Found

Replace with ChromePdfRenderer:

// Remove this
var doc = new Document(stream, new HtmlLoadOptions());

// Use this
var renderer = new ChromePdfRenderer();
var pdf = renderer.RenderHtmlAsPdf(htmlString);

// Remove this
var doc = new Document(stream, new HtmlLoadOptions());

// Use this
var renderer = new ChromePdfRenderer();
var pdf = renderer.RenderHtmlAsPdf(htmlString);

$vbLabelText $csharpLabel

Issue: TextFragmentAbsorber Not Found

Use direct text extraction:

// Remove this
var absorber = new TextFragmentAbsorber();
page.Accept(absorber);
string text = absorber.Text;

// Use this
var pdf = PdfDocument.FromFile("doc.pdf");
string text = pdf.ExtractAllText();

// Remove this
var absorber = new TextFragmentAbsorber();
page.Accept(absorber);
string text = absorber.Text;

// Use this
var pdf = PdfDocument.FromFile("doc.pdf");
string text = pdf.ExtractAllText();

$vbLabelText $csharpLabel

Issue: PdfFileEditor.Concatenate Not Available

Use PdfDocument.Merge():

// Remove this
var editor = new PdfFileEditor();
editor.Concatenate(files, output);

// Use this
var pdfs = files.Select(PdfDocument.FromFile).ToList();
var merged = PdfDocument.Merge(pdfs);
merged.SaveAs(output);

// Remove this
var editor = new PdfFileEditor();
editor.Concatenate(files, output);

// Use this
var pdfs = files.Select(PdfDocument.FromFile).ToList();
var merged = PdfDocument.Merge(pdfs);
merged.SaveAs(output);

$vbLabelText $csharpLabel

Post-Migration Checklist

After completing the code migration, verify the following:

Remove Aspose.PDF license files (.lic)
Verify HTML rendering quality (CSS Grid, Flexbox should now work correctly)
Test edge cases with large documents and complex CSS
Update page index references (1-based to 0-based)
Update Docker configurations if applicable
Update CI/CD pipelines with new license key configuration
Document new patterns for your team

Future-Proofing Your PDF Infrastructure

With .NET 10 on the horizon and C# 14 introducing new language features, choosing a PDF library with modern rendering capabilities ensures compatibility with evolving web standards. IronPDF's Chromium engine renders the same HTML/CSS that works in modern browsers, meaning your PDF templates stay current as projects extend into 2025 and 2026—without the CSS limitations of Aspose.PDF's Flying Saucer engine.

Additional Resources

Migrating from Aspose.PDF to IronPDF transforms your PDF codebase from an outdated HTML rendering engine to modern Chromium-based rendering. The elimination of MemoryStream wrappers, simplified text extraction, and superior CSS3 support deliver immediate productivity gains while reducing long-term licensing costs from annual subscriptions to a one-time investment.

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.

...

How to Migrate from BitMiracle Docotic PDF to IronPDF in C#

How to Migrate from Apryse PDF to I...

How to Migrate from Aspose.PDF to IronPDF in C#

Why Migrate Away from Aspose.PDF?

Cost Comparison

HTML Rendering Engine Comparison

Documented Performance Issues

Aspose.PDF vs. IronPDF: Key Differences

Pre-Migration Preparation

Prerequisites

Audit Aspose.PDF Usage

Breaking Changes to Anticipate

Step-by-Step Migration Process

Step 1: Update NuGet Packages

Step 2: Update Namespace References

Step 3: Update License Configuration

Complete API Migration Reference

Core Class Mapping

Document Operations

HTML to PDF Conversion

Code Migration Examples

HTML String to PDF

HTML File to PDF

Merging Multiple PDFs

Text Extraction

Adding Watermarks

Password Protection

Headers and Footers

Critical Migration Notes

Page Indexing Change

License File to Code Key

ASP.NET Core Integration

Dependency Injection Configuration

Performance Optimization

Troubleshooting Common Migration Issues

Issue: HtmlLoadOptions Not Found

Issue: TextFragmentAbsorber Not Found

Issue: PdfFileEditor.Concatenate Not Available

Post-Migration Checklist

Future-Proofing Your PDF Infrastructure

Additional Resources

Related Articles

How to Migrate from PDFmyURL to IronPDF in C#

How to Migrate from PuppeteerSharp to IronPDF in C#

How to Migrate from PdfPig to IronPDF in C#

Next step: Start free 30-day Trial

Next step: Start free 30-day Trial

Trusted by Over 2 Million Engineers Worldwide