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AFRelationship in PDF/A – User Guide

What Is AFRelationship?

AFRelationship (Associated File Relationship) is a metadata property used in PDFs to describe the relationship between a PDF document and an embedded file (attachment).

It was introduced with the Associated Files (AF) mechanism in the PDF specification and is heavily used in modern PDF/A standards.

AFRelationship tells software and archives:

Why is this file attached to the PDF?

Without AFRelationship, an attachment may be considered invalid for PDF/A compliance.

Why AFRelationship Matters

When a file is embedded in a PDF/A document:

  • The attachment must have a MIME type.
  • The attachment should have a meaningful AFRelationship value.
  • PDF validators use AFRelationship to verify compliance.

Examples:

AttachmentAFRelationship
Original XML invoiceSource
Spreadsheet used to generate reportData
Alternative representation of contentAlternative
Supplementary informationSupplement
Unknown relationshipUnspecified

Full AFRelationship Value List

The PDF specification defines the following standard values.

1. Source

The embedded file is the source from which the PDF was generated.

Examples:

  • XML invoice attached to a PDF invoice
  • Word document used to create a PDF
  • CAD source file 
AFRelationship = Source

Typical Use Cases

  • ZUGFeRD invoices
  • Factur-X invoices
  • PDF generated from DOCX

2. Data

The attachment contains data referenced by the PDF.

Examples:

  • CSV datasets
  • XML transaction data
  • Measurement data
  • Database exports 
AFRelationship = Data

Typical Use Cases

  • Scientific reports
  • Financial reports
  • Engineering measurements

3. Alternative

The attachment represents the same information in another format.

Examples:

  • PDF + HTML version
  • PDF + XML representation
  • PDF + plain text version 
AFRelationship = Alternative

Typical Use Cases

  • Accessibility
  • Machine-readable versions
  • Multi-format archiving

4. Supplement

The attachment provides additional information.

Examples:

  • Reference materials
  • Supporting documents
  • Appendices
  • Manuals 
AFRelationship = Supplement

Typical Use Cases

  • Technical documentation
  • Engineering projects
  • Research archives

5. EncryptedPayload

The attachment contains encrypted content.

AFRelationship = EncryptedPayload

Used primarily in secure workflows.

Not commonly seen in PDF/A archival documents.

6. FormData

The attachment contains form submission data.

Examples:

  • XFDF
  • FDF
  • XML form export 
AFRelationship = FormData

Typical Use Cases

  • Interactive forms
  • Government forms
  • Enterprise workflows

7. Schema

The attachment contains schema definitions.

Examples:

  • XSD files
  • JSON schemas
  • Validation definitions 
AFRelationship = Schema

Typical Use Cases

  • XML-based document packages
  • Structured archives

8. Unspecified

Relationship is unknown or not declared.

AFRelationship = Unspecified

Use only when no other value accurately describes the relationship.

Many validators accept it, but archival best practice is to use a more specific value whenever possible.

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