PDF/A-1b, 2b, 2u, 3b or 3u: which PDF/A should I choose?

"Save as PDF/A" sounds like one choice until a menu offers you five. The names look like part numbers, and in a sense they are. Once you know how to read them, picking one takes seconds.

If you have not met PDF/A before, start with what PDF/A is.

Reading the name: a number and a letter

PDF/A-2b has two parts.

The number is the part of the standard, which is really its generation. Each part is built on a newer version of PDF and allows more.

The letter is the conformance level: how much of the document the standard promises to preserve.

The numbers: which generation

There is also a fourth part, PDF/A-4, published in 2020 and based on PDF 2.0. KovaPDF does not offer it.

The letters: what is preserved

• b (basic): the document will look exactly the same in the future. This is the level most requirements mean.
• u (Unicode): everything in b, plus every character is mapped to real text, so the file can always be searched and copied reliably.
• a (accessible): everything in u, plus a complete structure of tags describing headings, reading order and image descriptions, for screen readers.

KovaPDF offers b and u. It does not offer level a, because producing it means keeping a complete and correct tag structure through the conversion, and when pages have to be rebuilt that structure cannot be kept. A standard that passes for only some documents would be a promise the tool cannot keep.

Which one to choose

Why PDF/A-2b is the sensible default

It keeps your document looking the way it does today, including transparency and layers, which PDF/A-1 cannot hold. It is widely accepted by archives, courts and public bodies. And it is forgiving: it does not need every character mapped to text, which is where the "u" versions sometimes fail.

What choosing PDF/A-1b costs you

PDF/A-1 predates transparency in PDF, so anything see-through (drop shadows, faded overlays, some logos) has to be flattened into solid colour. Where transparency overlaps text, that text can end up as part of an image and stop being searchable. PDF/A-1 also cannot keep attachments or layers, and it has lower limits on some numbers inside the file, which occasionally makes a file fail that would pass as PDF/A-2b.

So choose it only when you are told to.

When a "u" version fails

Some PDFs use fonts that draw letters without recording which letters they are. The page looks right, but the file does not know that a particular shape is an "e". PDF/A-2b does not mind. PDF/A-2u and 3u require every character to be mapped, so a file like that cannot pass, and KovaPDF will say so and suggest PDF/A-2b instead, rather than hand you a file that fails.

PDF/A-3 and attached files

PDF/A-2 accepts attachments only if they are PDF/A files themselves. PDF/A-3 accepts attachments of any type, each recorded with its relationship to the document.

That is why some e-invoicing formats in Europe are built on PDF/A-3: a readable invoice for people, with the machine-readable invoice data attached as XML inside the same file.

To be clear about what the tool does: KovaPDF keeps existing attachments when you convert to PDF/A-3b or 3u. It does not create e-invoice data or the extra metadata particular e-invoicing formats need.

If your PDF has attachments and you choose any other standard, the tool tells you before converting that they will be removed.

Switching standards

Choose one, convert, and if you then find you needed another, choose Convert to another standard. The file is kept while you work (for about 30 minutes), so you do not have to upload it again.