> had to be printed AND available as PDF.

You just reminded me of a customer I was working for as a junior ERP consultant. They required us to have the proof a document was printed by a user.

I went far down the rabbit hole trying to come up with an end-to-end solution involving cryptographically signed messages sent to the printer, a physical QR code on the document to be scanned back for validation, and others convoluted half-backed contraptions. But I couldn't find an unhackable way to reconcile the state in the machine with the reality of the physical world.

A senior consultant solved it in 10 minutes. Showed them. They were ecstatic and we were paid.

What has he done? Just updated a "printed" column in the database to "True" when the user clicked the HTML "print" button.