# 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

PDF/A-3 (ISO 19005-3:2012) is the only PDF/A subset that allows embedded files of arbitrary type, which is what makes ZUGFeRD and Factur-X possible. Using PDF/A-2 or non-archival PDF means the embedded XML cannot be considered legally archived together with the human-readable invoice — a problem under §147 AO and most EU long-term storage regimes.

## 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

- Producing PDF/A-3a (accessibility variant) when the consumer expects PDF/A-3b (basic) — many corporate AP systems silently reject A-3a.
- Setting AFRelationship on the embedded file to "Source" or "Supplement" instead of the Factur-X-mandated "Data".
- 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?
A-3b (basic) is the most widely accepted for hybrid e-invoices. A-3u adds Unicode mapping; A-3a adds tagged-PDF accessibility. Pick A-3b unless the consumer explicitly requires A-3u or A-3a.

### Can I open a PDF/A-3 in any PDF reader?
Yes — PDF/A-3 files render in any standard PDF reader (Acrobat, browser viewers). Only specialised systems also extract and parse the embedded XML invoice.

## 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.