Reference
PDF/A error reference
What each PDF/A-1b failure means, why a document ends up with it, and what to do about it.
Each entry answers the question first, then gives the clause, the cause and the fix. If you have a document in front of you and want to know what is wrong with it, the validator runs in your browser and names the failing checks — nothing is uploaded. For background on the standard itself, start with the guides.
File structure
6.1.x — file header, trailer, xref, object framing, limits
Encrypted document
PDF/A forbids encryption of any kind, including permission-only owner passwords. Why, and how to produce an unencrypted archival copy.
Embedded files
PDF/A-1 forbids file attachments. Which parts allow them, and what to do with a document that has one.
Colour
6.2.2 OutputIntent, 6.2.3.x device colours, 6.2.9–10
Transparency
6.2.8 transfer functions, 6.4 soft masks/blend modes/alpha
Fonts
6.3.x embedding, subsets, metrics, encoding
Annotations
6.5.x annotation types and dictionaries
Actions
6.6.x action types and additional actions
Metadata
6.7.x XMP metadata, extension schemas, PDF/A identifier
gopdfrab runs 159 checks across 11 groups
This reference covers the failures real documents hit most often, not every registered check. The full registry is queryable from the library, and every issue reported by the validator carries its own clause and description.