Convert HTML to PDF/A for archiving in C#

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. 3Write the HTML

   Program.cs · lines 3–12 COPY

   string html = """
       <html lang="en">
       <head><title>Contract 2026-117</title></head>
       <body>
         <h1>Service contract 2026-117</h1>
         <p>Signed on 13 October 2026 between Contoso Ltd. and Fabrikam Inc.</p>
         <p>This copy is kept for the full retention period.</p>
       </body>
       </html>
       """;

   Any HTML converts to PDF/A. In your application this is usually a page rendered from a template, or a URL passed to ConvertUrl.

4. 4Choose the PDF/A level

   Program.cs · lines 14–17 COPY

   HtmlToPdf converter = new HtmlToPdf();
   
   // PDF/A-2b: archival output, with every font embedded
   converter.Options.PdfStandard = PdfStandard.PdfA2B;

   Options.PdfStandard = PdfStandard.PdfA2B writes the document as PDF/A-2b. The default, PdfStandard.Full, is a standard PDF with no conformance constraints.

5. 5Set the document metadata

   Program.cs · lines 19–22 COPY

   // document metadata, written into the archived file
   converter.Options.PdfDocumentInformation.Title = "Service contract 2026-117";
   converter.Options.PdfDocumentInformation.Author = "Contracts department";
   converter.Options.PdfDocumentInformation.Subject = "Signed service contract";

   Options.PdfDocumentInformation sets the title, author and subject recorded in the generated document, so the archived file describes itself.

6. 6Convert and save

   Program.cs · lines 24–26 COPY

   PdfDocument doc = converter.ConvertHtmlString(html);
   doc.Save("contract-pdfa2b.pdf");
   doc.Close();

   ConvertHtmlString returns the PDF/A document; Save writes contract-pdfa2b.pdf and Close releases it.

7. 7Run it

   terminal COPY

   dotnet run

   The program writes contract-pdfa2b.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;

string html = """
    <html lang="en">
    <head><title>Contract 2026-117</title></head>
    <body>
      <h1>Service contract 2026-117</h1>
      <p>Signed on 13 October 2026 between Contoso Ltd. and Fabrikam Inc.</p>
      <p>This copy is kept for the full retention period.</p>
    </body>
    </html>
    """;

HtmlToPdf converter = new HtmlToPdf();

// PDF/A-2b: archival output, with every font embedded
converter.Options.PdfStandard = PdfStandard.PdfA2B;

// document metadata, written into the archived file
converter.Options.PdfDocumentInformation.Title = "Service contract 2026-117";
converter.Options.PdfDocumentInformation.Author = "Contracts department";
converter.Options.PdfDocumentInformation.Subject = "Signed service contract";

PdfDocument doc = converter.ConvertHtmlString(html);
doc.Save("contract-pdfa2b.pdf");
doc.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.

PDF/A-1b for archives that require the first part

PdfStandard.PdfA is PDF/A-1b. Use it when an archive or a regulation asks for PDF/A-1 specifically. PDF/A-1b does not combine with PDF/UA: producing it rebuilds the document in a way that does not keep its logical structure. For an accessible PDF/A-1 file, use PDF/A-1a (PdfStandard.PdfA1A), which keeps it.

using SelectPdf.Universal;

static class PdfA1b
{
    public static void Run()
    {
        HtmlToPdf converter = new HtmlToPdf();

        // PdfStandard.PdfA is PDF/A-1b, for archives that accept only the first part
        converter.Options.PdfStandard = PdfStandard.PdfA;
        converter.Options.PdfDocumentInformation.Title = "Statement 2026-09";

        PdfDocument doc = converter.ConvertHtmlString(
            "<h1>Statement 2026-09</h1><p>Closing balance: 4,250.00</p>");
        doc.Save("statement-pdfa1b.pdf");
        doc.Close();
    }
}

PDF/A-3b with the source data embedded

PDF/A-3 is the level that may carry embedded files. AddAssociatedFile embeds a stream (or a file from disk) as an associated file, with a PdfAttachmentRelationship that says how it relates to the pages: here Source, the data the report was built from. Associated files are listed in the document's /AF array when a PDF/A-3 document is saved.

using System.Text;
using SelectPdf.Universal;

static class PdfA3bWithSource
{
    public static void Run()
    {
        string csv = "Region,Revenue\nEurope,1200000\nAmericas,900000\n";

        HtmlToPdf converter = new HtmlToPdf();

        // PDF/A-3 is the level that may carry embedded files
        converter.Options.PdfStandard = PdfStandard.PdfA3B;
        converter.Options.PdfDocumentInformation.Title = "Revenue by region";

        PdfDocument doc = converter.ConvertHtmlString(
            "<h1>Revenue by region</h1><p>Europe: 1,200,000<br>Americas: 900,000</p>");

        // embed the data the report was built from, as an associated file
        using (MemoryStream data = new MemoryStream(Encoding.UTF8.GetBytes(csv)))
        {
            doc.AddAssociatedFile(data, "revenue.csv", PdfAttachmentRelationship.Source,
                "text/csv", "Revenue data");
            doc.Save("revenue-pdfa3b.pdf");
        }

        doc.Close();
    }
}

Merge converted pages into a PDF/A document

new PdfDocument(PdfStandard.PdfA2B) creates an empty document that declares PDF/A-2b, and Append adds the converted pages to it. A PDF/A target takes pages only from documents of the same PDF/A part with at least the same conformance, so the sources are converted as PDF/A-2b too. Close the sources after the merged document is saved.

using SelectPdf.Universal;

static class MergeIntoPdfA
{
    public static void Run()
    {
        HtmlToPdf converter = new HtmlToPdf();
        converter.Options.PdfStandard = PdfStandard.PdfA2B;

        PdfDocument cover = converter.ConvertHtmlString("<h1>Case file 2026-31</h1>");
        PdfDocument body = converter.ConvertHtmlString("<h2>Correspondence</h2><p>Letter of 2 October 2026.</p>");

        // the target declares PDF/A-2b and accepts only PDF/A-2 sources
        PdfDocument archive = new PdfDocument(PdfStandard.PdfA2B);
        archive.Append(cover);
        archive.Append(body);
        archive.Save("case-file-pdfa2b.pdf");

        archive.Close();
        cover.Close();
        body.Close();
    }
}

Common problems and fixes.

Good to know.

• The PdfStandard enumeration selects the archiving standard: PDF/A-1 at levels B and A, PDF/A-2 and PDF/A-3 at levels B, U and A, and PDF/A-4 with its 4E and 4F variants. Source
• PDF/A documents require every font to be embedded. Source
• PDF/A-3 is the level that may carry embedded files, which is what hybrid electronic invoices are built on. Source
• PDF/A does not permit sound, movie and screen annotations, or link actions that launch an external file or run JavaScript; adding one raises an error that names the feature instead of producing a non-conformant file. Source
• A document created with a PDF/A standard takes pages only from documents of the same PDF/A part with at least the same conformance. Source