HTML to PDF in C#: convert a URL or an HTML string

Build it step by step.

1. 1Install the NuGet packages

   SelectPdf.Universal is the library. The native package carries the Chromium engine for one platform: add the one for the platform you run on.

   Windows x64 Linux x64 Linux ARM64 macOS · Apple Silicon
   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.win-x64

   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.linux-x64

   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.linux-arm64

   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.osx-arm64

2. 2Create a console app

   Any .NET 8 or .NET 10 project works. To follow along, create a console app, run the install commands above inside its folder, then replace Program.cs with the code below.

   terminal COPY

   dotnet new console -n PdfSample
   cd PdfSample

3. 3Create the converter

   Program.cs · lines 1–3 COPY

   using SelectPdf.Universal;
   
   HtmlToPdf converter = new HtmlToPdf();

   HtmlToPdf is the converter. One object can convert several pages, one after another.

4. 4Set A4 and 20 mm margins

   Program.cs · lines 5–11 COPY

   // A4 portrait with 20 mm margins (margins are in points: 20 mm = 57 pt)
   converter.Options.PdfPageSize = PdfPageSize.A4;
   converter.Options.PdfPageOrientation = PdfPageOrientation.Portrait;
   converter.Options.MarginTop = 57;
   converter.Options.MarginBottom = 57;
   converter.Options.MarginLeft = 57;
   converter.Options.MarginRight = 57;

   PdfPageSize and PdfPageOrientation set the paper. Margins are in points (1/72 inch): 20 mm is 57 points. The defaults are A4 portrait with no margins, so set what your document needs.

5. 5Convert a web page by URL

   Program.cs · lines 13–16 COPY

   // 1. a web page, by URL
   PdfDocument page = converter.ConvertUrl("https://selectpdf.com");
   page.Save("webpage.pdf");
   page.Close();

   ConvertUrl loads the page in the Chromium engine, runs its scripts and styles, and returns a PdfDocument. Save writes it and Close releases it.

6. 6Convert an HTML string

   Program.cs · lines 18–26 COPY

   // 2. an HTML string; the base URL resolves relative images, styles and links
   string html = """
       <img src="img/selectpdf-logo-h128.png" alt="SelectPdf" height="40">
       <h1>Invoice #1042</h1>
       <p>Issued to Contoso Ltd on 12 October 2026.</p>
       """;
   PdfDocument invoice = converter.ConvertHtmlString(html, "https://selectpdf.com/");
   invoice.Save("invoice.pdf");
   invoice.Close();

   ConvertHtmlString takes HTML you build yourself, such as a template filled with your data. The second argument is the base URL: the relative image path img/selectpdf-logo-h128.png is loaded from https://selectpdf.com/. Without external references, the one-argument overload is enough.

7. 7Run it

   terminal COPY

   dotnet run

   The program writes webpage.pdf to the working folder. Without a license key, every page carries a trial watermark; set GlobalProperties.LicenseKey before the first conversion to remove it.

The complete Program.cs.

This is the exact file our samples pipeline compiled and ran on Linux ARM64 and Linux x64 and macOS ARM64 and Windows x64 to produce the output on this page.

using SelectPdf.Universal;

HtmlToPdf converter = new HtmlToPdf();

// A4 portrait with 20 mm margins (margins are in points: 20 mm = 57 pt)
converter.Options.PdfPageSize = PdfPageSize.A4;
converter.Options.PdfPageOrientation = PdfPageOrientation.Portrait;
converter.Options.MarginTop = 57;
converter.Options.MarginBottom = 57;
converter.Options.MarginLeft = 57;
converter.Options.MarginRight = 57;

// 1. a web page, by URL
PdfDocument page = converter.ConvertUrl("https://selectpdf.com");
page.Save("webpage.pdf");
page.Close();

// 2. an HTML string; the base URL resolves relative images, styles and links
string html = """
    <img src="img/selectpdf-logo-h128.png" alt="SelectPdf" height="40">
    <h1>Invoice #1042</h1>
    <p>Issued to Contoso Ltd on 12 October 2026.</p>
    """;
PdfDocument invoice = converter.ConvertHtmlString(html, "https://selectpdf.com/");
invoice.Save("invoice.pdf");
invoice.Close();

Open the project on GitHub → this program and the variations below, ready to dotnet run

The PDF it produces.

Variations you will need next.

Each variation is a separate file in the same project, compiled and run with the program above.

Use the page's print stylesheet

Many sites hide navigation and ads in @media print rules. CssMediaType = HtmlToPdfCssMediaType.Print applies them, as the browser's Print command does.

using SelectPdf.Universal;

static class PrintStylesheet
{
    public static void Run()
    {
        HtmlToPdf converter = new HtmlToPdf();
        converter.Options.PdfPageSize = PdfPageSize.A4;

        // use the page's @media print rules, as the browser's Print command does
        converter.Options.CssMediaType = HtmlToPdfCssMediaType.Print;

        PdfDocument doc = converter.ConvertUrl("https://selectpdf.com");
        doc.Save("webpage-print.pdf");
        doc.Close();
    }
}

Wait for content that JavaScript adds

Charts and data grids often appear after the page has loaded. ConversionDelay waits a number of seconds before rendering, and NavigationTimeout fails a page that never finishes loading instead of waiting forever.

using SelectPdf.Universal;

static class WaitForJavaScript
{
    public static void Run()
    {
        // content that a script adds half a second after the page loads, like a chart or a data grid
        string html = """
            <h1>Sales report</h1>
            <div id="chart">loading...</div>
            <script>
              setTimeout(() => document.getElementById("chart").textContent = "Q3 revenue: 1.2M", 500);
            </script>
            """;

        HtmlToPdf converter = new HtmlToPdf();
        converter.Options.ConversionDelay = 2;      // seconds to wait after the page loads
        converter.Options.NavigationTimeout = 30;   // seconds before a page that never loads fails

        PdfDocument doc = converter.ConvertHtmlString(html);
        doc.Save("report.pdf");
        doc.Close();
    }
}

Convert asynchronously, with a timeout

In a web app or a service, ConvertUrlAsync and ConvertHtmlStringAsync hold no thread while the page loads. A CancellationToken stops a conversion that takes too long. Save() without a file name returns the PDF as bytes.

using SelectPdf.Universal;

static class ConvertAsync
{
    public static async Task Run()
    {
        // in a web app or service: await the conversion, and give up after 30 seconds
        using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(30));

        HtmlToPdf converter = new HtmlToPdf();
        PdfDocument doc = await converter.ConvertUrlAsync("https://selectpdf.com", timeout.Token);

        byte[] pdf = doc.Save();   // the PDF as bytes, for a response or a database
        doc.Close();

        await File.WriteAllBytesAsync("webpage-async.pdf", pdf);
    }
}

Common problems and fixes.

Good to know.

• Margins are set in points: 1 point is 1/72 inch, so 20 mm is 57 points. Source
• With a base URL, ConvertHtmlString resolves relative images, style sheets and links against it. Source
• ConversionDelay waits after the page loads, for content that scripts add; NavigationTimeout limits the wait for a slow page. Source
• The converter renders with the screen CSS media type by default; Print applies the page's print styles. Source