PDF/A versions: 1a, 1b, 2b, 3b
The number is the version of the standard, the letter is the conformance level. Here is how to read them and which one to choose.
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Parts and levels
| Version | Year | What changes |
|---|---|---|
| PDF/A-1 | 2005 | Based on PDF 1.4: no transparency, layers or JPEG 2000 |
| PDF/A-2 | 2011 | Based on PDF 1.7: allows transparency, layers, JPEG 2000 and PDF/A attachments |
| PDF/A-3 | 2012 | Like PDF/A-2, plus attachments of any format, such as XML |
| PDF/A-4 | 2020 | Based on PDF 2.0; drops the a, b, u letters and comes as PDF/A-4, 4e and 4f |
The level: b (basic) preserves the appearance; a (accessible) also requires the tagged structure — headings, paragraphs, reading order; u (Unicode, in versions 2 and 3) requires all text to be extractable.
PDF/A-1b vs PDF/A-2b
PDF/A-2b is the right default: it accepts the transparency and layers that today's software produces all the time, so more documents convert without becoming images. Choose PDF/A-1b only when the recipient asks for it, or when it accepts only PDF up to version 1.6 — the USPTO's Patent Center is one example.
«1a or 1b?» — 1b is almost always enough. Level «a» needs a document tagged when it was created; conversion cannot add it.
PDF/A-3 and e-invoices
PDF/A-3 exists mostly for documents that carry structured data, such as the European hybrid e-invoice (Factur-X, ZUGFeRD): a PDF/A-3 with an XML file attached. Converting it to another version would drop the XML, so our converter leaves those files untouched.
Frequently asked questions
What is PDF/A-1b?
The first version of the PDF/A standard (2005, based on PDF 1.4) at the basic level, which guarantees the appearance of the document. It forbids transparency and layers.
PDF/A-1a vs 1b: what is the difference?
Both preserve the appearance. 1a also requires a tagged, accessible structure, which must be built when the document is created. When both are accepted, 1b is the practical choice.