PDF/A-3

Also called PDF/A-3b, PDF/A-3a, PDF/A-3u

PDF/A-3 is an ISO archival PDF format whose distinguishing feature is that it permits arbitrary embedded files. That is the hook Factur-X hangs the invoice XML on, which is why the standard requires it rather than any PDF.

Standard: ISO 19005-3
Conformance levels: 3a, 3b and 3u, all conformant Factur-X
Key property: Permits arbitrary embedded files
What we generate: PDF/A-3b

Why the format is specified at all

PDF/A exists so a document opens the same way in twenty years: fonts embedded, no external dependencies, no JavaScript. The 3 in PDF/A-3 is the revision that allows arbitrary file attachments, which earlier PDF/A revisions forbade.

Without that allowance there would be nowhere compliant to put the XML. So the requirement is not bureaucratic: PDF/A-3 is the only archival PDF that can legally carry the payload.

3a, 3b and 3u are all conformant, whatever a vendor tells you

The letter is the conformance level. 3b is the baseline and guarantees visual reproduction. 3u adds a guarantee that text can be extracted as Unicode. 3a adds structural tagging for accessibility.

All three are conformant Factur-X. If someone tells you that you specifically need 3u, ask why, because it is the sort of claim that gets repeated without a source. We generate 3b, and that is a deliberate limit worth naming: a customer whose own policy demands 3a or 3u cannot be served by our generation path today.

It fails invisibly

A PDF that is not PDF/A-3 looks identical on screen to one that is. Exporting from a normal design tool will not produce one, and nothing about the result will warn you.

Checking it properly means running the ISO conformance rules, which is why that check is the server side opt in on our validator rather than part of the browser pass. veraPDF is the engine, and it is not something that reasonably runs in a browser tab.

Why it matters

It is one of the three things that must be true at once, and the only one you cannot see by opening the file.
A generator that embeds XML into an ordinary PDF produces something that looks right, opens right and is not a Factur-X invoice.

Check it on your own file

Check PDF/A-3 conformance
The ISO check runs on our server via veraPDF, as an opt in per file. The browser side pass covers the XML and the embedding, not this.

Common questions

Do I need PDF/A-3b specifically?: No. PDF/A-3a, 3b and 3u are all conformant Factur-X. 3b is the baseline and the most common.
Can I turn a normal PDF into a PDF/A-3?: Yes, with a conversion step, but embedding XML into an ordinary PDF is not enough on its own. The container itself has to satisfy the ISO rules, and that is only checkable by running them.