Naked Security has a great story about a couple whose real estate fraud was revealed by some document forensics. The couple produced documents as evidence of real estate deals in 1995 and 2004, but the documents used fonts that only became available in 2007.
This reminds me of the story of the NSA contractor who got caught leaking classified information, because invisible dots on pages she printed identified her printer.
Both stories are fascinating to me, because they show how much extra information shows up in our documents, and we don’t even realize it. These would make great twists in a story if a character needed to disprove a document or identify its owner.