[Feature Request] Creating digital stamps on documents

Description Hello, I'd like to suggest a stamping feature. Many proprietary DMS have that and it allows the user to stamp a document digitally, just like with a real stamp. This stamp would be embedded onto the document. Use case It is typically used for stamps like "PAID [date], [bank account]" or "DELIVERED [date]". I personally stamp all my incoming documents with a so called Eingangsstempel (german), which stamps the date of when I received the letter onto the document. Then, for example, when I have to pay something, I put a stamp on it again with "PAID [date of payment]", so I always have it right on the document in case I need that info. This feature could also be used for signing a document digitally (like not real certificate signing, but signing it with your name). Current alternative and it's drawbacks Of course, all those infos could be put into the note field in Paperless, but these informations are then lost wh…