PDF/A Compliance

Generate archival-grade PDFs that conform to the PDF/A-2 and PDF/A-3 standards (ISO 19005). FolioPDF handles XMP metadata, font embedding, color space requirements, and structure tagging automatically.

Overview

PDF/A is an ISO-standardized subset of PDF designed for long-term preservation of electronic documents. It guarantees that a PDF will render identically decades from now, regardless of which viewer or operating system is used. PDF/A achieves this by restricting certain PDF features (external references, encryption, JavaScript) and mandating others (font embedding, color profiles, XMP metadata).

FolioPDF supports six PDF/A conformance levels across two standard versions:

Quick Start

Set the conformance level in DocumentSettings:

using FolioPDF;
using FolioPDF.Fluent;
using FolioPDF.Helpers;
using FolioPDF.Infrastructure;

Document.Create(doc =>
{
    doc.Page(page =>
    {
        page.Size(PageSizes.A4);
        page.Margin(50);
        page.Content().Text("This is a PDF/A-2b document.").FontSize(14);
    });
})
.WithSettings(new DocumentSettings
{
    PdfAConformance = PdfAConformance.PdfA_2B
})
.WithMetadata(new DocumentMetadata
{
    Title = "Annual Report 2026",
    Author = "Finance Department",
    Language = "en-US"
})
.GeneratePdf("report-pdfa.pdf");

Understanding the Conformance Levels

Level A vs Level B vs Level U

Each PDF/A version (2 and 3) comes in three "conformance levels" that add progressively stricter requirements:

PDF/A-2 vs PDF/A-3

The only difference between PDF/A-2 and PDF/A-3 is file attachments:

• PDF/A-2 does NOT allow arbitrary file attachments.
• PDF/A-3 allows embedding arbitrary files (XML, CSV, images, other PDFs) as document-level attachments with a mandatory /AFRelationship entry.

This makes PDF/A-3 the required standard for:

• ZUGFeRD (German e-invoicing) — embeds a factur-x.xml file
• Factur-X (French/EU e-invoicing) — same XML standard
• Hybrid documents that carry both a human-readable PDF and machine-readable data

Required Metadata

PDF/A mandates certain metadata fields. FolioPDF sets defaults for most, but you should provide meaningful values:

Document.Create(doc => { /* ... */ })
.WithMetadata(new DocumentMetadata
{
    Title = "Q1 Financial Report",     // Required by PDF/A
    Author = "Jane Smith",             // Strongly recommended
    Subject = "Quarterly financials",  // Optional but recommended
    Keywords = "finance, Q1, 2026",    // Optional
    Language = "en-US",                // Required by PDF/A-a levels
    Creator = "Report Generator v3.0", // Optional
})
.WithSettings(new DocumentSettings
{
    PdfAConformance = PdfAConformance.PdfA_2A
})
.GeneratePdf("q1-report.pdf");

Semantic Tagging for Level A

Level A (PDF/A-2a, PDF/A-3a) requires a complete structure tree. FolioPDF's auto-tagging system handles most content automatically, but headings must be tagged explicitly:

Auto-Tagging (Default Behavior)

When DocumentSettings.AutoTagDocument is true (the default), FolioPDF automatically wraps:

• Text blocks as <P> (Paragraph)
• Images as <Figure>
• Tables as <Table>
• Headers and footers as Artifacts (excluded from the structure tree)

This is sufficient for level B and U. Level A requires explicit heading tags:

Explicit Semantic Tags

doc.Page(page =>
{
    page.Size(PageSizes.A4);
    page.Margin(50);

    page.Content().Column(col =>
    {
        col.Spacing(10);

        // Heading level 1
        col.Item().SemanticHeader1().Text("Annual Report").FontSize(24).Bold();

        // Paragraph (auto-tagged, but can be explicit)
        col.Item().SemanticParagraph().Text("This report covers the fiscal year 2026.");

        // Heading level 2
        col.Item().SemanticHeader2().Text("Revenue").FontSize(18).Bold();
        col.Item().SemanticParagraph().Text("Total revenue: $4.2M");

        // Semantic list
        col.Item().SemanticList().Column(list =>
        {
            list.Item().SemanticListItem().Row(row =>
            {
                row.AutoItem().SemanticListLabel().Text("1. ");
                row.RelativeItem().SemanticListItemBody().Text("Q1: $1.0M");
            });
            list.Item().SemanticListItem().Row(row =>
            {
                row.AutoItem().SemanticListLabel().Text("2. ");
                row.RelativeItem().SemanticListItemBody().Text("Q2: $1.1M");
            });
        });

        // Image with alt text (required for level A)
        col.Item().SemanticFigure("Chart showing quarterly revenue growth")
            .Image(File.ReadAllBytes("revenue-chart.png"));

        // Semantic table
        col.Item().SemanticTable().Table(table =>
        {
            table.ColumnsDefinition(c =>
            {
                c.RelativeColumn();
                c.RelativeColumn();
            });
            table.Cell().SemanticTableHeaderCell().Text("Quarter").Bold();
            table.Cell().SemanticTableHeaderCell().Text("Revenue").Bold();
            table.Cell().SemanticTableCell().Text("Q1");
            table.Cell().SemanticTableCell().Text("$1.0M");
        });
    });
});

Available Semantic Tags

Choosing the Right Level

Combining with ZUGFeRD / Factur-X

ZUGFeRD and Factur-X are European e-invoicing standards that require a PDF/A-3b document with an embedded XML invoice file. FolioPDF supports the full workflow:

using FolioPDF;
using FolioPDF.Fluent;
using FolioPDF.Fluent.DocumentOperation;
using FolioPDF.Helpers;
using FolioPDF.Infrastructure;

// 1. Generate the visual invoice as PDF/A-3b
byte[] pdfBytes = Document.Create(doc =>
{
    doc.Page(page =>
    {
        page.Size(PageSizes.A4);
        page.Margin(40);
        page.Content().Column(col =>
        {
            col.Spacing(8);
            col.Item().Text("Invoice #2026-0042").FontSize(20).Bold();
            col.Item().Text("Date: 2026-04-11");
            col.Item().Text("Total: EUR 1,234.56").FontSize(16);
        });
    });
})
.WithSettings(new DocumentSettings
{
    PdfAConformance = PdfAConformance.PdfA_3B
})
.WithMetadata(new DocumentMetadata
{
    Title = "Invoice 2026-0042",
    Author = "Acme Corp Billing"
})
.GeneratePdf();

// 2. Attach the Factur-X XML and set the AFRelationship
byte[] xmlInvoice = File.ReadAllBytes("factur-x.xml");

byte[] finalPdf = DocumentOperation.FromBytes(pdfBytes)
    .AddAttachment(new DocumentAttachment
    {
        Name = "factur-x.xml",
        Data = xmlInvoice,
        MimeType = "text/xml",
        Description = "Factur-X invoice data",
        Relationship = "Alternative"    // PDF/A-3 AFRelationship
    })
    .ExtendMetadata(zugferdXmpXml)      // XMP with Factur-X extension schemas
    .ToBytes();

Validation with veraPDF

veraPDF is the industry-standard open-source PDF/A validator. FolioPDF's conformance tests use it to verify every generated document.

Install veraPDF

# Download from https://verapdf.org/software/
# Or via package manager (Linux):
sudo apt install verapdf

# macOS (Homebrew):
brew install verapdf

Validate a Document

# Validate against auto-detected profile
verapdf report-pdfa.pdf

# Validate against a specific profile
verapdf --profile 2b report-pdfa.pdf

# Machine-readable output
verapdf --format json report-pdfa.pdf

Programmatic Validation

// Run veraPDF as a process
var process = new System.Diagnostics.Process
{
    StartInfo = new System.Diagnostics.ProcessStartInfo
    {
        FileName = "verapdf",
        Arguments = "--format json report-pdfa.pdf",
        RedirectStandardOutput = true,
        UseShellExecute = false
    }
};

process.Start();
string output = process.StandardOutput.ReadToEnd();
process.WaitForExit();

bool isCompliant = output.Contains("\"compliant\": true");
Console.WriteLine($"PDF/A compliant: {isCompliant}");

What FolioPDF Handles Automatically

When a PDF/A conformance level is set, FolioPDF's rendering pipeline automatically:

• Embeds all fonts as subsetted OpenType/TrueType programs (no external font references)
• Includes ToUnicode CMaps for all text (required by levels U and A)
• Sets the output intent to sRGB IEC61966-2.1 (the default RGB color space for screen)
• Generates XMP metadata with the correct pdfaid:part and pdfaid:conformance entries
• Marks the document as tagged with /MarkInfo << /Marked true >>
• Sets the document language from DocumentMetadata.Language
• Auto-tags content elements as P, Figure, and Table when AutoTagDocument is true
• Strips JavaScript and multimedia (forbidden in PDF/A)
• Ensures all images use supported color spaces (sRGB, Grayscale)

Configuration Reference

var settings = new DocumentSettings
{
    // PDF/A conformance level (default: None)
    PdfAConformance = PdfAConformance.PdfA_2A,

    // Auto-tag content for structure tree (default: true)
    // Set to false only if you provide all semantic tags manually
    AutoTagDocument = true,

    // Image compression quality (default: High)
    // PDF/A allows JPEG compression; lower quality = smaller files
    ImageCompressionQuality = ImageCompressionQuality.High,

    // Document content direction (default: LeftToRight)
    ContentDirection = ContentDirection.LeftToRight,
};

Common Validation Issues

Known Limitations

• PDF/A-1 is not supported. FolioPDF targets PDF/A-2 and PDF/A-3 (ISO 19005-2/3, based on PDF 1.7). PDF/A-1 (ISO 19005-1, based on PDF 1.4) is an older standard with stricter constraints that are incompatible with modern Skia output.
• CMYK output intent is not yet supported. FolioPDF uses sRGB as the output intent. Professional print workflows that require ISO Coated v2 or similar CMYK profiles should convert the output in a post-processing step.
• Embedded file validation for PDF/A-3 does not validate the content of attached files. The attachment is embedded with correct metadata, but the PDF/A validator does not check whether the XML is valid Factur-X.
• Auto-tagging does not detect headings. Font-size heuristics are unreliable, so auto-tagging only produces P, Figure, and Table tags. Use SemanticHeader1 through SemanticHeader6 explicitly for heading structure.