FO.NET vs IronPDF: Technical Comparison Guide

HTML to PDF Conversion

The most fundamental operation demonstrates the model difference between XSL-FO and HTML approaches.

FO.NET:

// NuGet: Install-Package Fonet
using Fonet;
using Fonet.Render.Pdf;
using System.IO;
using System.Xml;

class Program
{
    static void Main()
    {
        // FoNet requires XSL-FO format, not HTML
        // First convert HTML to XSL-FO (manual process)
        string xslFo = @"<?xml version='1.0' encoding='utf-8'?>
            <fo:root xmlns:fo='http://www.w3.org/1999/XSL/Format'>
                <fo:layout-master-set>
                    <fo:simple-page-master master-name='page'>
                        <fo:region-body/>
                    </fo:simple-page-master>
                </fo:layout-master-set>
                <fo:page-sequence master-reference='page'>
                    <fo:flow flow-name='xsl-region-body'>
                        <fo:block>Hello World</fo:block>
                    </fo:flow>
                </fo:page-sequence>
            </fo:root>";

        FonetDriver driver = FonetDriver.Make();
        driver.Render(new StringReader(xslFo), 
            new FileStream("output.pdf", FileMode.Create));
    }
}

// NuGet: Install-Package Fonet
using Fonet;
using Fonet.Render.Pdf;
using System.IO;
using System.Xml;

class Program
{
    static void Main()
    {
        // FoNet requires XSL-FO format, not HTML
        // First convert HTML to XSL-FO (manual process)
        string xslFo = @"<?xml version='1.0' encoding='utf-8'?>
            <fo:root xmlns:fo='http://www.w3.org/1999/XSL/Format'>
                <fo:layout-master-set>
                    <fo:simple-page-master master-name='page'>
                        <fo:region-body/>
                    </fo:simple-page-master>
                </fo:layout-master-set>
                <fo:page-sequence master-reference='page'>
                    <fo:flow flow-name='xsl-region-body'>
                        <fo:block>Hello World</fo:block>
                    </fo:flow>
                </fo:page-sequence>
            </fo:root>";

        FonetDriver driver = FonetDriver.Make();
        driver.Render(new StringReader(xslFo), 
            new FileStream("output.pdf", FileMode.Create));
    }
}

IronPDF:

// NuGet: Install-Package IronPdf
using IronPdf;

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

// NuGet: Install-Package IronPdf
using IronPdf;

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

The contrast is clear. FO.NET requires verbose XSL-FO markup with XML namespace declarations, fo:root, fo:layout-master-set, fo:simple-page-master, fo:page-sequence, fo:flow, and fo:block elements—all before producing a simple "Hello World" text. The code comment explicitly notes: "FoNet requires XSL-FO format, not HTML."

IronPDF creates a renderer, passes standard HTML, renders to PDF, and saves—four simple lines using syntax developers already know.

For advanced HTML rendering options, explore the HTML to PDF conversion guide.

URL to PDF Conversion

Converting web pages to PDF reveals a critical capability gap.

FO.NET:

// NuGet: Install-Package Fonet
using Fonet;
using System.IO;
using System.Net;

class Program
{
    static void Main()
    {
        // FoNet does not support URL rendering directly
        // Must manually download, convert HTML to XSL-FO, then render
        string url = "https://example.com";
        string html = new WebClient().DownloadString(url);

        // Manual conversion from HTML to XSL-FO required (complex)
        string xslFo = ConvertHtmlToXslFo(html); // Not built-in

        FonetDriver driver = FonetDriver.Make();
        driver.Render(new StringReader(xslFo), 
            new FileStream("webpage.pdf", FileMode.Create));
    }

    static string ConvertHtmlToXslFo(string html)
    {
        // Custom implementation required
        throw new System.NotImplementedException();
    }
}

// NuGet: Install-Package Fonet
using Fonet;
using System.IO;
using System.Net;

class Program
{
    static void Main()
    {
        // FoNet does not support URL rendering directly
        // Must manually download, convert HTML to XSL-FO, then render
        string url = "https://example.com";
        string html = new WebClient().DownloadString(url);

        // Manual conversion from HTML to XSL-FO required (complex)
        string xslFo = ConvertHtmlToXslFo(html); // Not built-in

        FonetDriver driver = FonetDriver.Make();
        driver.Render(new StringReader(xslFo), 
            new FileStream("webpage.pdf", FileMode.Create));
    }

    static string ConvertHtmlToXslFo(string html)
    {
        // Custom implementation required
        throw new System.NotImplementedException();
    }
}

IronPDF:

// NuGet: Install-Package IronPdf
using IronPdf;

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

// NuGet: Install-Package IronPdf
using IronPdf;

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

FO.NET explicitly does not support URL rendering. The code comments state: "FoNet does not support URL rendering directly" and "Manual conversion from HTML to XSL-FO required (complex)." The ConvertHtmlToXslFo() method throws NotImplementedException because this conversion is not built-in and would require custom implementation.

IronPDF provides native RenderUrlAsPdf() functionality that handles URL fetching, JavaScript execution, and rendering in a single method call—three lines of code versus a complex, unimplemented workflow.

Learn more about URL rendering in the URL to PDF documentation.

PDF with Custom Settings

Configuring page dimensions and margins demonstrates the configuration approach differences.

FO.NET:

// NuGet: Install-Package Fonet
using Fonet;
using Fonet.Render.Pdf;
using System.IO;

class Program
{
    static void Main()
    {
        // FoNet settings are configured in XSL-FO markup
        string xslFo = @"<?xml version='1.0' encoding='utf-8'?>
            <fo:root xmlns:fo='http://www.w3.org/1999/XSL/Format'>
                <fo:layout-master-set>
                    <fo:simple-page-master master-name='A4' 
                        page-height='297mm' page-width='210mm'
                        margin-top='20mm' margin-bottom='20mm'
                        margin-left='25mm' margin-right='25mm'>
                        <fo:region-body/>
                    </fo:simple-page-master>
                </fo:layout-master-set>
                <fo:page-sequence master-reference='A4'>
                    <fo:flow flow-name='xsl-region-body'>
                        <fo:block font-size='14pt'>Custom PDF</fo:block>
                    </fo:flow>
                </fo:page-sequence>
            </fo:root>";

        FonetDriver driver = FonetDriver.Make();
        driver.Render(new StringReader(xslFo), 
            new FileStream("custom.pdf", FileMode.Create));
    }
}

// NuGet: Install-Package Fonet
using Fonet;
using Fonet.Render.Pdf;
using System.IO;

class Program
{
    static void Main()
    {
        // FoNet settings are configured in XSL-FO markup
        string xslFo = @"<?xml version='1.0' encoding='utf-8'?>
            <fo:root xmlns:fo='http://www.w3.org/1999/XSL/Format'>
                <fo:layout-master-set>
                    <fo:simple-page-master master-name='A4' 
                        page-height='297mm' page-width='210mm'
                        margin-top='20mm' margin-bottom='20mm'
                        margin-left='25mm' margin-right='25mm'>
                        <fo:region-body/>
                    </fo:simple-page-master>
                </fo:layout-master-set>
                <fo:page-sequence master-reference='A4'>
                    <fo:flow flow-name='xsl-region-body'>
                        <fo:block font-size='14pt'>Custom PDF</fo:block>
                    </fo:flow>
                </fo:page-sequence>
            </fo:root>";

        FonetDriver driver = FonetDriver.Make();
        driver.Render(new StringReader(xslFo), 
            new FileStream("custom.pdf", FileMode.Create));
    }
}

IronPDF:

// NuGet: Install-Package IronPdf
using IronPdf;
using IronPdf.Engines.Chrome;

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        renderer.RenderingOptions.PaperSize = PdfPaperSize.A4;
        renderer.RenderingOptions.MarginTop = 20;
        renderer.RenderingOptions.MarginBottom = 20;
        renderer.RenderingOptions.MarginLeft = 25;
        renderer.RenderingOptions.MarginRight = 25;

        string html = "<h1 style='font-size:14pt'>Custom PDF</h1>";
        var pdf = renderer.RenderHtmlAsPdf(html);
        pdf.SaveAs("custom.pdf");
    }
}

// NuGet: Install-Package IronPdf
using IronPdf;
using IronPdf.Engines.Chrome;

class Program
{
    static void Main()
    {
        var renderer = new ChromePdfRenderer();
        renderer.RenderingOptions.PaperSize = PdfPaperSize.A4;
        renderer.RenderingOptions.MarginTop = 20;
        renderer.RenderingOptions.MarginBottom = 20;
        renderer.RenderingOptions.MarginLeft = 25;
        renderer.RenderingOptions.MarginRight = 25;

        string html = "<h1 style='font-size:14pt'>Custom PDF</h1>";
        var pdf = renderer.RenderHtmlAsPdf(html);
        pdf.SaveAs("custom.pdf");
    }
}

The code comment in FO.NET explicitly states: "FoNet settings are configured in XSL-FO markup." Page size, margins, and formatting are embedded within the XML structure as attributes on fo:simple-page-master. This means configuration is intertwined with content in a verbose XML format.

IronPDF separates configuration from content using programmatic RenderingOptions properties. Settings like PaperSize, MarginTop, MarginBottom, MarginLeft, and MarginRight are set on the renderer object, while content remains clean HTML.

Core Class Mapping

XSL-FO to RenderingOptions Mapping

XSL-FO Elements to HTML Mapping

FO.NET Strengths

• Direct XSL-FO Conversion: Optimized specifically for XSL-FO to PDF conversion
• Open Source: Apache 2.0 license—free to use, modify, and distribute
• Precise Control: XSL-FO provides detailed control over document layout

FO.NET Considerations

• Obsolete Technology: XSL-FO specification has no updates since 2006
• Requires XSL-FO Knowledge: Less than 1% of developers have expertise
• No HTML Support: Cannot render HTML or CSS content
• Abandoned: No active maintenance or security updates
• Windows Only: System.Drawing dependencies prevent cross-platform use
• No URL Rendering: Cannot directly convert web pages
• Limited Documentation: Resources are outdated

IronPDF Strengths

• HTML/CSS Standard: Uses web technologies over 98% of developers already know
• Modern Rendering: Chromium engine with full CSS3 and JavaScript support
• Active Development: Monthly releases with new features and security patches
• Cross-Platform: True support for Windows, Linux, and macOS
• Direct URL Rendering: Native RenderUrlAsPdf() capability
• Professional Features: Headers, footers, watermarks, security—all built-in
• Comprehensive Resources: Extensive tutorials and documentation

IronPDF Considerations

• Commercial License: Requires license for production use
• Different Paradigm: XSL-FO templates need conversion to HTML