Migrate from Foxit PDF SDK to IronPDF: (.NET Guide)

The Foxit PDF Challenges

Foxit PDF SDK is a strong enterprise-level library, but it comes with significant complexity that can slow down development:

1. Complex Licensing System: Multiple products, SKUs, and license types (per-developer, per-server, OEM, etc.) make it difficult to choose the right option for your project.

2. Enterprise Pricing: Pricing is tailored for large organizations and can be prohibitive for smaller teams or individual developers.

3. Manual Installation: Foxit PDF SDK requires manual DLL references or private NuGet feeds—there's no simple public NuGet package available.

4. Verbose API: Library initialization with Library.Initialize(), error code checking, and explicit Library.Release() calls add substantial boilerplate to every operation.

5. Separate HTML Conversion Add-on: HTML to PDF conversion requires an additional add-on purchase—it's not included in the base SDK.

6. Complex Configuration: Settings require detailed object configuration (e.g., HTML2PDFSettingData) with multiple properties.

7. C++ Heritage: API patterns reflect C++ origins, feeling less natural in modern C# applications.

Foxit PDF vs IronPDF Comparison

Cost-Benefit Analysis

Moving from Foxit PDF to IronPDF offers tangible development benefits: reduced complexity through simpler APIs, faster development with intuitive methods, modern .NET compatibility including async/await and LINQ support, an HTML-first approach that uses existing web skills, and all-inclusive features without separate add-on purchases. As you plan for .NET 10 and C# 14 adoption through 2025 and 2026, IronPDF provides a future-proof foundation for PDF generation.

Prerequisites

1. .NET Environment: IronPDF supports .NET Framework 4.6.2+, .NET Core 3.1+, .NET 5/6/7/8/9+
2. NuGet Access: Ensure you can install packages from NuGet
3. License Key: Obtain your IronPDF license key for production use from ironpdf.com

Backup Your Project

# Create a backup branch
git checkout -b pre-ironpdf-migration
git add .
git commit -m "Backup before Foxit PDF SDK to IronPDF migration"

# Create a backup branch
git checkout -b pre-ironpdf-migration
git add .
git commit -m "Backup before Foxit PDF SDK to IronPDF migration"

Identify All Foxit PDF Usage

# Find all Foxit PDF SDK references
grep -r "foxit\|PDFDoc\|PDFPage\|Library.Initialize\|Library.Release" --include="*.cs" --include="*.csproj" .

# Find Foxit DLL references
find . -name "*.csproj" | xargs grep -l "Foxit\|fsdk"

# Find all Foxit PDF SDK references
grep -r "foxit\|PDFDoc\|PDFPage\|Library.Initialize\|Library.Release" --include="*.cs" --include="*.csproj" .

# Find Foxit DLL references
find . -name "*.csproj" | xargs grep -l "Foxit\|fsdk"

Document Current Functionality

Before migration, catalog:

• Which Foxit PDF features you use (HTML conversion, annotations, forms, security)
• License key locations and initialization code
• Custom configurations and settings
• Error handling patterns using ErrorCode enums

Step 1: Update NuGet Packages

# Foxit PDF SDK typically requires manual removal of DLL references
# Check your .csproj for Foxit references and remove them

# Install IronPDF
dotnet add package IronPdf

# Foxit PDF SDK typically requires manual removal of DLL references
# Check your .csproj for Foxit references and remove them

# Install IronPDF
dotnet add package IronPdf

If you have Foxit PDF references in .csproj, remove them manually:

<!-- Remove these manually -->
<Reference Include="fsdk_dotnet">
    <HintPath>..\libs\Foxit\fsdk_dotnet.dll</HintPath>
</Reference>

<!-- Remove these manually -->
<Reference Include="fsdk_dotnet">
    <HintPath>..\libs\Foxit\fsdk_dotnet.dll</HintPath>
</Reference>

Step 2: Update Namespaces

// Before (Foxit PDF)
using foxit;
using foxit.common;
using foxit.common.fxcrt;
using foxit.pdf;
using foxit.pdf.annots;
using foxit.addon.conversion;

// After (IronPDF)
using IronPdf;
using IronPdf.Rendering;
using IronPdf.Editing;

// Before (Foxit PDF)
using foxit;
using foxit.common;
using foxit.common.fxcrt;
using foxit.pdf;
using foxit.pdf.annots;
using foxit.addon.conversion;

// After (IronPDF)
using IronPdf;
using IronPdf.Rendering;
using IronPdf.Editing;

Step 3: Initialize IronPDF

One of the most significant improvements in this Foxit PDF migration is eliminating the complex initialization and cleanup pattern:

// Before (Foxit PDF)
string sn = "YOUR_SERIAL_NUMBER";
string key = "YOUR_LICENSE_KEY";
ErrorCode error_code = Library.Initialize(sn, key);
if (error_code != ErrorCode.e_ErrSuccess)
{
    throw new Exception("Failed to initialize Foxit PDF SDK");
}
// ... your code ...
Library.Release();  // Don't forget this!

// After (IronPDF)
IronPdf.License.LicenseKey = "YOUR-IRONPDF-LICENSE-KEY";
// That's it! No Release() needed

// Before (Foxit PDF)
string sn = "YOUR_SERIAL_NUMBER";
string key = "YOUR_LICENSE_KEY";
ErrorCode error_code = Library.Initialize(sn, key);
if (error_code != ErrorCode.e_ErrSuccess)
{
    throw new Exception("Failed to initialize Foxit PDF SDK");
}
// ... your code ...
Library.Release();  // Don't forget this!

// After (IronPDF)
IronPdf.License.LicenseKey = "YOUR-IRONPDF-LICENSE-KEY";
// That's it! No Release() needed

Step 4: Basic Conversion Pattern

// Before (Foxit PDF)
Library.Initialize(sn, key);
HTML2PDFSettingData settings = new HTML2PDFSettingData();
settings.page_width = 612.0f;
settings.page_height = 792.0f;
using (HTML2PDF html2pdf = new HTML2PDF(settings))
{
    html2pdf.Convert(htmlContent, "output.pdf");
}
Library.Release();

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

// Before (Foxit PDF)
Library.Initialize(sn, key);
HTML2PDFSettingData settings = new HTML2PDFSettingData();
settings.page_width = 612.0f;
settings.page_height = 792.0f;
using (HTML2PDF html2pdf = new HTML2PDF(settings))
{
    html2pdf.Convert(htmlContent, "output.pdf");
}
Library.Release();

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

Namespace Mapping

Core Class Mapping

PDFDoc Methods

HTML2PDF / Conversion

Watermark Settings

Example 1: HTML to PDF Conversion

Before (Foxit PDF SDK):

// NuGet: Install-Package Foxit.SDK
using Foxit.SDK;
using Foxit.SDK.Common;
using Foxit.SDK.PDFConversion;
using System;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        HTML2PDFSettingData settingData = new HTML2PDFSettingData();
        settingData.page_width = 612.0f;
        settingData.page_height = 792.0f;
        settingData.page_mode = HTML2PDFPageMode.e_HTML2PDFPageModeSinglePage;

        using (HTML2PDF html2pdf = new HTML2PDF(settingData))
        {
            html2pdf.Convert("<html><body><h1>Hello World</h1></body></html>", "output.pdf");
        }

        Library.Release();
    }
}

// NuGet: Install-Package Foxit.SDK
using Foxit.SDK;
using Foxit.SDK.Common;
using Foxit.SDK.PDFConversion;
using System;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        HTML2PDFSettingData settingData = new HTML2PDFSettingData();
        settingData.page_width = 612.0f;
        settingData.page_height = 792.0f;
        settingData.page_mode = HTML2PDFPageMode.e_HTML2PDFPageModeSinglePage;

        using (HTML2PDF html2pdf = new HTML2PDF(settingData))
        {
            html2pdf.Convert("<html><body><h1>Hello World</h1></body></html>", "output.pdf");
        }

        Library.Release();
    }
}

After (IronPDF):

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

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf("<html><body><h1>Hello World</h1></body></html>");
        pdf.SaveAs("output.pdf");
    }
}

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

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf("<html><body><h1>Hello World</h1></body></html>");
        pdf.SaveAs("output.pdf");
    }
}

The IronPDF approach reduces 15+ lines of configuration code to just 4 lines. No library initialization, no explicit cleanup, no complex settings objects. For more HTML rendering options, see the HTML to PDF documentation.

Example 2: URL to PDF Conversion

Before (Foxit PDF SDK):

// NuGet: Install-Package Foxit.SDK
using Foxit.SDK;
using Foxit.SDK.Common;
using Foxit.SDK.PDFConversion;
using System;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        HTML2PDFSettingData settingData = new HTML2PDFSettingData();
        settingData.page_width = 612.0f;
        settingData.page_height = 792.0f;
        settingData.page_mode = HTML2PDFPageMode.e_HTML2PDFPageModeSinglePage;

        using (HTML2PDF html2pdf = new HTML2PDF(settingData))
        {
            html2pdf.ConvertFromURL("https://www.example.com", "output.pdf");
        }

        Library.Release();
    }
}

// NuGet: Install-Package Foxit.SDK
using Foxit.SDK;
using Foxit.SDK.Common;
using Foxit.SDK.PDFConversion;
using System;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        HTML2PDFSettingData settingData = new HTML2PDFSettingData();
        settingData.page_width = 612.0f;
        settingData.page_height = 792.0f;
        settingData.page_mode = HTML2PDFPageMode.e_HTML2PDFPageModeSinglePage;

        using (HTML2PDF html2pdf = new HTML2PDF(settingData))
        {
            html2pdf.ConvertFromURL("https://www.example.com", "output.pdf");
        }

        Library.Release();
    }
}

After (IronPDF):

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

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderUrlAsPdf("https://www.example.com");
        pdf.SaveAs("output.pdf");
    }
}

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

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderUrlAsPdf("https://www.example.com");
        pdf.SaveAs("output.pdf");
    }
}

IronPDF's built-in Chromium engine handles JavaScript execution, CSS rendering, and dynamic content automatically. Learn more about URL to PDF conversion.

Example 3: Adding Watermarks

Before (Foxit PDF SDK):

// NuGet: Install-Package Foxit.SDK
using Foxit.SDK;
using Foxit.SDK.Common;
using Foxit.SDK.PDFDoc;
using System;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        using (PDFDoc doc = new PDFDoc("input.pdf"))
        {
            doc.Load("");

            Watermark watermark = new Watermark(doc, "Confidential", 
                new Font(Font.StandardID.e_StdIDHelvetica), 48.0f, 0xFF0000FF);

            WatermarkSettings settings = new WatermarkSettings();
            settings.flags = Watermark.e_WatermarkFlagASPageContents;
            settings.position = Watermark.Position.e_PosCenter;
            settings.rotation = -45.0f;
            settings.opacity = 0.5f;

            watermark.SetSettings(settings);
            watermark.InsertToAllPages();

            doc.SaveAs("output.pdf", PDFDoc.SaveFlags.e_SaveFlagNoOriginal);
        }

        Library.Release();
    }
}

// NuGet: Install-Package Foxit.SDK
using Foxit.SDK;
using Foxit.SDK.Common;
using Foxit.SDK.PDFDoc;
using System;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        using (PDFDoc doc = new PDFDoc("input.pdf"))
        {
            doc.Load("");

            Watermark watermark = new Watermark(doc, "Confidential", 
                new Font(Font.StandardID.e_StdIDHelvetica), 48.0f, 0xFF0000FF);

            WatermarkSettings settings = new WatermarkSettings();
            settings.flags = Watermark.e_WatermarkFlagASPageContents;
            settings.position = Watermark.Position.e_PosCenter;
            settings.rotation = -45.0f;
            settings.opacity = 0.5f;

            watermark.SetSettings(settings);
            watermark.InsertToAllPages();

            doc.SaveAs("output.pdf", PDFDoc.SaveFlags.e_SaveFlagNoOriginal);
        }

        Library.Release();
    }
}

After (IronPDF):

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

class Program
{
    static void Main()
    {
        var pdf = PdfDocument.FromFile("input.pdf");
        pdf.ApplyWatermark(new TextStamper()
        {
            Text = "Confidential",
            FontSize = 48,
            Opacity = 50,
            Rotation = -45,
            VerticalAlignment = VerticalAlignment.Middle,
            HorizontalAlignment = HorizontalAlignment.Center
        });
        pdf.SaveAs("output.pdf");
    }
}

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

class Program
{
    static void Main()
    {
        var pdf = PdfDocument.FromFile("input.pdf");
        pdf.ApplyWatermark(new TextStamper()
        {
            Text = "Confidential",
            FontSize = 48,
            Opacity = 50,
            Rotation = -45,
            VerticalAlignment = VerticalAlignment.Middle,
            HorizontalAlignment = HorizontalAlignment.Center
        });
        pdf.SaveAs("output.pdf");
    }
}

IronPDF's TextStamper provides intuitive property-based configuration instead of separate settings objects and manual page iteration. See the complete watermarking documentation for additional options.

Example 4: URL to PDF with Headers and Footers

Before (Foxit PDF SDK):

using foxit;
using foxit.addon.conversion;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        try
        {
            HTML2PDFSettingData settings = new HTML2PDFSettingData();
            settings.page_width = 595.0f;  // A4
            settings.page_height = 842.0f;
            settings.page_margin_top = 100.0f;
            settings.page_margin_bottom = 100.0f;

            // Foxit PDF SDK has limited header/footer support
            // Often requires post-processing or additional code

            using (HTML2PDF html2pdf = new HTML2PDF(settings))
            {
                html2pdf.ConvertFromURL("https://www.example.com", "webpage.pdf");
            }
        }
        finally
        {
            Library.Release();
        }
    }
}

using foxit;
using foxit.addon.conversion;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        try
        {
            HTML2PDFSettingData settings = new HTML2PDFSettingData();
            settings.page_width = 595.0f;  // A4
            settings.page_height = 842.0f;
            settings.page_margin_top = 100.0f;
            settings.page_margin_bottom = 100.0f;

            // Foxit PDF SDK has limited header/footer support
            // Often requires post-processing or additional code

            using (HTML2PDF html2pdf = new HTML2PDF(settings))
            {
                html2pdf.ConvertFromURL("https://www.example.com", "webpage.pdf");
            }
        }
        finally
        {
            Library.Release();
        }
    }
}

After (IronPDF):

using IronPdf;

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        renderer.RenderingOptions.PaperSize = PdfPaperSize.A4;
        renderer.RenderingOptions.PrintHtmlBackgrounds = true;
        renderer.RenderingOptions.WaitFor.RenderDelay(3000);  // Wait for JS

        // Built-in header/footer support
        renderer.RenderingOptions.HtmlHeader = new HtmlHeaderFooter()
        {
            HtmlFragment = "<div style='text-align:center; font-size:12pt;'>Company Report</div>",
            DrawDividerLine = true
        };

        renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter()
        {
            HtmlFragment = "<div style='text-align:right; font-size:10pt;'>Page {page} of {total-pages}</div>",
            DrawDividerLine = true
        };

        var pdf = renderer.RenderUrlAsPdf("https://www.example.com");
        pdf.SaveAs("webpage.pdf");
    }
}

using IronPdf;

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        renderer.RenderingOptions.PaperSize = PdfPaperSize.A4;
        renderer.RenderingOptions.PrintHtmlBackgrounds = true;
        renderer.RenderingOptions.WaitFor.RenderDelay(3000);  // Wait for JS

        // Built-in header/footer support
        renderer.RenderingOptions.HtmlHeader = new HtmlHeaderFooter()
        {
            HtmlFragment = "<div style='text-align:center; font-size:12pt;'>Company Report</div>",
            DrawDividerLine = true
        };

        renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter()
        {
            HtmlFragment = "<div style='text-align:right; font-size:10pt;'>Page {page} of {total-pages}</div>",
            DrawDividerLine = true
        };

        var pdf = renderer.RenderUrlAsPdf("https://www.example.com");
        pdf.SaveAs("webpage.pdf");
    }
}

IronPDF provides native headers and footers support with HTML styling and dynamic page number placeholders.

Example 5: PDF Security and Encryption

Before (Foxit PDF SDK):

using foxit;
using foxit.pdf;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        try
        {
            using (PDFDoc doc = new PDFDoc("input.pdf"))
            {
                doc.LoadW("");

                StdSecurityHandler securityHandler = new StdSecurityHandler();
                securityHandler.Initialize(
                    StdSecurityHandler.EncryptAlgorithm.e_CipherAES,
                    "user_password",
                    "owner_password",
                    PDFDoc.Permission.e_PermPrint | PDFDoc.Permission.e_PermModify,
                    128);

                doc.SetSecurityHandler(securityHandler);
                doc.SaveAs("encrypted.pdf", (int)PDFDoc.SaveFlags.e_SaveFlagNoOriginal);
            }
        }
        finally
        {
            Library.Release();
        }
    }
}

using foxit;
using foxit.pdf;

class Program
{
    static void Main()
    {
        Library.Initialize("sn", "key");

        try
        {
            using (PDFDoc doc = new PDFDoc("input.pdf"))
            {
                doc.LoadW("");

                StdSecurityHandler securityHandler = new StdSecurityHandler();
                securityHandler.Initialize(
                    StdSecurityHandler.EncryptAlgorithm.e_CipherAES,
                    "user_password",
                    "owner_password",
                    PDFDoc.Permission.e_PermPrint | PDFDoc.Permission.e_PermModify,
                    128);

                doc.SetSecurityHandler(securityHandler);
                doc.SaveAs("encrypted.pdf", (int)PDFDoc.SaveFlags.e_SaveFlagNoOriginal);
            }
        }
        finally
        {
            Library.Release();
        }
    }
}

After (IronPDF):

using IronPdf;

class Program
{
    static void Main()
    {
        var pdf = PdfDocument.FromFile("input.pdf");

        // Set passwords
        pdf.SecuritySettings.OwnerPassword = "owner_password";
        pdf.SecuritySettings.UserPassword = "user_password";

        // Set permissions
        pdf.SecuritySettings.AllowUserPrinting = IronPdf.Security.PdfPrintSecurity.FullPrintRights;
        pdf.SecuritySettings.AllowUserEdits = IronPdf.Security.PdfEditSecurity.EditAll;
        pdf.SecuritySettings.AllowUserCopyPasteContent = true;
        pdf.SecuritySettings.AllowUserAnnotations = true;

        pdf.SaveAs("encrypted.pdf");
    }
}

using IronPdf;

class Program
{
    static void Main()
    {
        var pdf = PdfDocument.FromFile("input.pdf");

        // Set passwords
        pdf.SecuritySettings.OwnerPassword = "owner_password";
        pdf.SecuritySettings.UserPassword = "user_password";

        // Set permissions
        pdf.SecuritySettings.AllowUserPrinting = IronPdf.Security.PdfPrintSecurity.FullPrintRights;
        pdf.SecuritySettings.AllowUserEdits = IronPdf.Security.PdfEditSecurity.EditAll;
        pdf.SecuritySettings.AllowUserCopyPasteContent = true;
        pdf.SecuritySettings.AllowUserAnnotations = true;

        pdf.SaveAs("encrypted.pdf");
    }
}

Reuse ChromePdfRenderer

For optimal performance during your Foxit PDF migration, reuse the ChromePdfRenderer instance—it's thread-safe:

// GOOD - Reuse renderer (thread-safe)
public class PdfService
{
    private static readonly ChromePdfRenderer _renderer = new ChromePdfRenderer();

    public byte[] Generate(string html) => _renderer.RenderHtmlAsPdf(html).BinaryData;
}

// BAD - Creates new instance each time
public byte[] GenerateBad(string html)
{
    var renderer = new ChromePdfRenderer();  // Wasteful
    return renderer.RenderHtmlAsPdf(html).BinaryData;
}

// GOOD - Reuse renderer (thread-safe)
public class PdfService
{
    private static readonly ChromePdfRenderer _renderer = new ChromePdfRenderer();

    public byte[] Generate(string html) => _renderer.RenderHtmlAsPdf(html).BinaryData;
}

// BAD - Creates new instance each time
public byte[] GenerateBad(string html)
{
    var renderer = new ChromePdfRenderer();  // Wasteful
    return renderer.RenderHtmlAsPdf(html).BinaryData;
}

Unit Conversion Helper

Foxit PDF SDK uses points; IronPDF uses millimeters. Use this helper during migration:

public static class UnitConverter
{
    public static double PointsToMm(double points) => points * 0.352778;
    public static double MmToPoints(double mm) => mm / 0.352778;
    public static double InchesToMm(double inches) => inches * 25.4;
}

// Usage: Convert Foxit's 72 points (1 inch) to IronPDF millimeters
renderer.RenderingOptions.MarginTop = UnitConverter.PointsToMm(72); // ~25.4mm

public static class UnitConverter
{
    public static double PointsToMm(double points) => points * 0.352778;
    public static double MmToPoints(double mm) => mm / 0.352778;
    public static double InchesToMm(double inches) => inches * 25.4;
}

// Usage: Convert Foxit's 72 points (1 inch) to IronPDF millimeters
renderer.RenderingOptions.MarginTop = UnitConverter.PointsToMm(72); // ~25.4mm

Proper Resource Disposal

// GOOD - Using statement for automatic cleanup
using (var pdf = PdfDocument.FromFile("large.pdf"))
{
    string text = pdf.ExtractAllText();
}  // pdf is disposed automatically

// GOOD - Using statement for automatic cleanup
using (var pdf = PdfDocument.FromFile("large.pdf"))
{
    string text = pdf.ExtractAllText();
}  // pdf is disposed automatically

Issue 1: Library.Initialize() Not Found

Problem: Library.Initialize() doesn't exist in IronPDF.

Solution: IronPDF uses a simpler initialization pattern:

// Foxit PDF
Library.Initialize(sn, key);

// IronPDF - just set license key once at startup
IronPdf.License.LicenseKey = "YOUR-KEY";

// Foxit PDF
Library.Initialize(sn, key);

// IronPDF - just set license key once at startup
IronPdf.License.LicenseKey = "YOUR-KEY";

Issue 2: ErrorCode Handling

Problem: Code checks ErrorCode.e_ErrSuccess but IronPDF doesn't have this.

Solution: Use standard .NET exception handling:

// Foxit PDF
ErrorCode err = doc.LoadW("");
if (err != ErrorCode.e_ErrSuccess) { /* handle error */ }

// IronPDF
try
{
    var pdf = PdfDocument.FromFile("input.pdf");
}
catch (IOException ex)
{
    Console.WriteLine($"Failed to load PDF: {ex.Message}");
}

// Foxit PDF
ErrorCode err = doc.LoadW("");
if (err != ErrorCode.e_ErrSuccess) { /* handle error */ }

// IronPDF
try
{
    var pdf = PdfDocument.FromFile("input.pdf");
}
catch (IOException ex)
{
    Console.WriteLine($"Failed to load PDF: {ex.Message}");
}

Issue 3: PDFDoc.Close() Not Found

Problem: doc.Close() method doesn't exist in IronPDF.

Solution: Use Dispose() or using statements:

// Foxit PDF
doc.Close();

// IronPDF
pdf.Dispose();
// or better: wrap in using statement

// Foxit PDF
doc.Close();

// IronPDF
pdf.Dispose();
// or better: wrap in using statement

Pre-Migration

• Inventory all Foxit PDF SDK features used
• Document license key locations
• Note all Library.Initialize() and Library.Release() calls
• List custom settings (page sizes, margins, etc.)
• Identify error handling patterns using ErrorCode
• Backup project to version control
• Obtain IronPDF license key

Package Migration

• Remove Foxit PDF SDK DLL references from .csproj
• Remove any private NuGet feed configurations
• Install IronPdf NuGet package: dotnet add package IronPdf
• Update namespace imports
• Set IronPDF license key at startup

Code Migration

• Remove Library.Initialize() and Library.Release() calls
• Replace ErrorCode checks with try/catch
• Replace PDFDoc with PdfDocument
• Replace HTML2PDF with ChromePdfRenderer
• Update page access from GetPage(i) to Pages[i]
• Replace SaveAs(path, flags) with SaveAs(path)
• Replace Close() with Dispose() or using statements
• Update watermark code to use TextStamper
• Convert units from points to millimeters

Testing

• Verify HTML to PDF output matches expectations
• Test PDF loading and text extraction
• Verify merge functionality
• Check watermark appearance
• Test security/encryption features
• Validate form field operations
• Performance testing

Post-Migration

• Delete Foxit PDF SDK DLLs
• Remove Foxit-related configuration files
• Update documentation
• Clean up unused helper code

migration.