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PDF/A explained: which version to pick and how to check it
A court, an archive or a tax portal asks for “PDF/A” and your file is rejected. PDF/A is simply PDF with rules that make it readable decades from now. Here is what those rules are, which version to pick, and how to check a file before you upload it.
PDF/A is an ISO standard (ISO 19005) for PDFs meant to be archived: everything needed to display the file must be inside it, and anything that could stop working later is banned. If the recipient names a version, use that one. If not, PDF/A-2b is the common choice, PDF/A-2u if the text must be searchable and copyable, and PDF/A-3 when you need to embed other files such as an invoice’s XML. Check the result with veraPDF, a free validator.
What makes a PDF a PDF/A
A normal PDF can rely on things outside itself: a font installed on your computer, a colour profile, a link, a script. Ten years later those may be gone. PDF/A forbids that kind of dependency:
- Fonts must be embedded, at least the characters used.
- Colours must be device-independent, with an output colour profile inside the file.
- No encryption or passwords, no JavaScript, no audio or video, no references to external content.
- Metadata in XMP, including the claim of which PDF/A part and level the file follows.
The four parts
| Part | Published | Based on | What it adds |
|---|---|---|---|
| PDF/A-1 (ISO 19005-1) | 2005 | PDF 1.4 | The original. No transparency, no layers. |
| PDF/A-2 (ISO 19005-2) | 2011 | PDF 1.7 (ISO 32000-1) | JPEG 2000, transparency, layers, embedded PDF/A files. |
| PDF/A-3 (ISO 19005-3) | 2012 | PDF 1.7 | Embedding any file type, such as XML, CSV or a spreadsheet. Used by hybrid e-invoices like ZUGFeRD and Factur-X. |
| PDF/A-4 (ISO 19005-4) | 2020 | PDF 2.0 (ISO 32000-2) | Drops the a/b/u levels; adds PDF/A-4f (embedded files) and PDF/A-4e (engineering, 3D). |
A newer part doesn’t replace an older one. A file that follows PDF/A-1 is still a valid PDF/A-1 file today.
The letters: a, b and u
- b (basic): the file will look the same in the future. The minimum, and enough for most scans.
- u (Unicode): also guarantees the text can be extracted and searched correctly. Available in parts 2 and 3.
- a (accessible): also requires a tagged structure, reading order and alternative text, for screen readers. The hardest to produce from existing files.
Which one to choose
- Whatever the recipient asks for. Courts, archives and portals often name an exact part and level. Follow it, even if it’s an old one.
- No instructions: PDF/A-2b is widely accepted and supports modern files.
- The text must be searchable: PDF/A-2u, after running OCR on scans.
- You need to attach source data, like an e-invoice XML: PDF/A-3.
- Accessibility is required: PDF/A-2a, ideally from a source document that was already tagged.
How to check a file for free
veraPDF is a free, open-source validator backed by the PDF Association and the PDF/A community. It checks a file against the part and level it claims, and lists every rule it breaks. Acrobat Pro’s Preflight can also validate. Don’t trust a file just because its metadata says “PDF/A”: that’s only the claim.
PDF/A and signatures
Converting to PDF/A rewrites the file, so it invalidates any digital signature already in it. Convert first, then sign. A signature added to a PDF/A file as an incremental update keeps the file valid PDF/A, as long as the signature itself follows the rules.
Keepsign makes PDF/A-2b copies on iPhone, iPad and Mac, with fonts and colour profile embedded and the claim in the metadata. In our tests, the copies passed veraPDF 1.30.3: 41 out of 41 files. It always makes a copy, so your original and its signatures stay as they were, and it warns if the original is signed. It can also make an archive package: the PDF/A plus a report of what was checked, for documents you need to keep for years. PDF/A is part of Keepsign Pro. Conversions in Keepsign.
Sources
- PDF Association, “ISO 19005 (PDF/A)”, pdfa.org/resource/iso-19005-pdfa
- veraPDF, the PDF/A validator, verapdf.org
- ISO 19005-1:2005, ISO 19005-2:2011, ISO 19005-3:2012 and ISO 19005-4:2020, iso.org.
- Keepsign validation run with veraPDF 1.30.3, November 5, 2026.