PDF/A-3
PDF/A-3 is ISO 19005-3, and it differs from PDF/A-2 in exactly one respect: an embedded file no longer has to be a PDF. Everything else, including the PDF 1.7 base version and every other rule UniPDF checks, is identical between the two parts.
That one change is the point. It makes PDF/A-3 the container format for hybrid documents, where a human-readable PDF and a machine-readable payload travel as one file. Electronic invoicing is the common case: ZUGFeRD, Factur-X and the related standards all specify a PDF/A-3 file with an XML invoice attached.
Three profiles cover it: pdfa.NewProfile3B, pdfa.NewProfile3U and
pdfa.NewProfile3A.
The rules that still apply to attachments are the structural ones. A file specification
with an EF entry has to carry F and UF file names, and an AFRelationship entry
saying how the attachment relates to the document. Rule 6.8-2 covers the first and
6.8-3 the second. Missing either fails validation regardless of what the attachment
contains. Adding the attachment itself is not part of PDF/A conversion; see
attachments.
Where to look
| Guide | Covers |
|---|---|
| Apply PDF/A-3 | Converting a document to PDF/A-3 and keeping attachments. |
| Validate PDF/A-3 | Checking a file against 3A, 3B and 3U. |
The shared mechanics, the full profile list and the conformance levels are covered on the PDF/A section page.