Underpinning all digital security systems is encryption. If your prospective document security system does not use this, then forget it because it is just smoke and mirrors. Encryption is the technology that hides documents from those who are not authorized, and verifies that the content the originator created is unchanged.
If you are an authorized recipient of encrypted information you have the ability to do anything you like with that information once you have removed the encryption. That is the Achilles’ heel. The recipient of documents that have been encrypted can go on to use them in any way they wish, and to alter them in any way they wish. That does not mean they can pretend that someone else originated them. And that is a valuable protection, provided you can be bothered to look closely at the authenticity of documents you receive. But judging by the number of people taken in by fake messages from financial institutions or amazing offers from Nigeria, maybe looking to see if a document is real is not a top priority.
Encryption therefore is just the building block of document security but has limited controls.