# PDF/A-3

PDF archival standard allowing embedded files (used for ZUGFeRD/Factur-X).

## Definition

PDF archival standard allowing embedded files (used for ZUGFeRD/Factur-X).

## Why this term matters

ZUGFeRD and Factur-X packages use PDF/A-3 as the container for a readable PDF and embedded CII XML. Passing the PDF/A and package checks confirms file structure, not legal retention by itself. Retention also depends on the applicable tax rules, storage controls, and the original invoice record.

## Explanation

Lets you keep a human-readable PDF and embed the XML invoice as an attachment.

Commonly used for long-term archiving and audits.

## Common mistakes

- Choosing a PDF/A-3 conformance level without checking the exact package version, profile, and recipient requirements.
- Copying AFRelationship from a generic PDF/A example instead of using the value permitted by the exact ZUGFeRD or Factur-X package and profile.
- Failing the PDF/A-3 conformance check because the PDF embeds fonts that are not subset/embedded fully or includes non-PDF/A-conformant transparency.
- Embedding the XML as an annotation/file attachment without registering it in the AF (Associated Files) array — readers cannot find it.

## Frequently asked questions

### What is the difference between PDF/A-2 and PDF/A-3?
PDF/A-2 (ISO 19005-2) and PDF/A-3 share the same rendering rules, but PDF/A-3 additionally allows embedded files of any MIME type. That single difference is why hybrid e-invoices like ZUGFeRD and Factur-X are based on PDF/A-3.

### Do I need PDF/A-3a, A-3b, or A-3u?
Use the conformance level required by the exact ZUGFeRD or Factur-X package and recipient. Do not choose a level by popularity alone.

### Can I open a PDF/A-3 in any PDF reader?
Most current PDF readers can show the visual layer. Extracting and processing the embedded XML requires software that supports associated files and the invoice package.

## Related resources

- [ZUGFeRD guide](/resources/compliance/zugferd-format)

## Related terms

- [ZUGFeRD](/resources/glossary/zugferd): Hybrid e-invoice format: a human-readable PDF with embedded XML.
- [Factur-X](/resources/glossary/factur-x): French hybrid e-invoice format, aligned with ZUGFeRD and EN 16931 profiles.