> The answer seems obvious to me: [1, 2, 3]

Yeah, that would be nice, but it is SO RARE, I've not even heard of that being possible, let alone how to get at the metadata with godforsaken readers like Acrobat. I mean, I've used pdf's since literally the beginning. Never knew that was a feature.

I think this is all the consequence of the failure of XML and it's promise of its related formatting and transformation tooling. The 90's vision was beautiful: semantic documents with separate presentation and transformation tools/languages, all machine readable, versioned, importable, extensible. But no. Here we are in the year 2025. And what do we got? pdf, html, markdown, json, yaml, and csv.

There are solid reasons why XML failed, but the reasons were human and organizational, and NOT because of the well-thought-out tech.