If someone told me there was cryptographic proof of job experience in their PDF, I would probably just believe them because it’d be a weird thing to lie about.

In theory your (old) boss could sign part of your CV with a certificate obtained from any CA participating in Adobe's AATL programme. If you use the software right, you could have different ranges signed by different people/companies. Because only a small component gets signed, you'd need them to sign text saying "Jane Doe worked at X corp and did their job well" as a signed line like "software developer" can be yanked out and placed into other PDF documents (simplifying a little here).

I'm not sure if there's software out there to make that process easy, but the format allows for it. The format also allows for someone to produce and sign one version and someone else to adjust that version and sign the new changes.

Funnily enough, the PDF signature actually has a field to refer to a (picture of) a readable signature in the file, so software can jot down a scan of a signature that automatically inserts cryptographic proof.

In practice I've never seen PDFs signed with more than one signature. PDF readers from anyone but Adobe seem to completely ignore signatures unless you manually open the document properties, but Adobe Reader will show you a banner saying "document signed by XYZ" when you open a signed document.

Encrypted (and hidden) embedded information, e. g. documents, signatures, certificates, watermarks, and the like. To (legally-binding) standards, e. g. for notary, et cetera.