veraPDF
veraPDF is a free program that opens a document and says whether it really follows the rule it claims to follow.
In more detail
A file can say anything about itself. A line inside it may claim it follows the archival rule. That claim costs nothing to write and proves nothing.
veraPDF reads the whole file and checks the claim against the published rule, point by point. It comes back with a plain yes, or with the list of what is wrong and where. Nobody has to take the maker's word for it, which is the entire point.
What it does on a real document
Before a change enters the library or the service, veraPDF is run on both sides. On the library's, the example behind the accessible document shown here is written twice more — once asking for the accessibility rules built on the newer standard, once asking for an archival level — and each result is handed over. On the service's, every document claiming the same archival part goes to it in a single pass, and whatever those documents carry is pulled back out by a separate program and compared, byte for byte, with the file that went in. A refusal on either side stops the check where it stands.
And every document published here is compared, byte for byte, with what its own example writes, so the file you download is the file that was measured.
When it refuses, it names the rule it is refusing under. A font that is in the file but missing a piece of its identity card, a colour with nothing saying what it should look like, a picture with no description: each is a separate line of the report, with the exact part of the document it concerns.
Where it comes from, and why
It was built in the middle of the 2010s by a group led by the Open Preservation Foundation and the PDF Association, paid for by a European Union programme called PREFORMA. The aim of that programme was to give libraries, archives and museums checking tools they own rather than rent.
That is why it is free and why anybody may read how it works. An archive that has to open a file decades from now cannot depend on a company still selling a program decades from now. It has since learned to check accessible documents as well as archival ones.
See it on a finished document
An archivable PDF/A-3 form The page that goes further on this word