When is a documentary not a documentary? When it is put in the hands of a master like Orson Welles. F for Fake is often gets dismissed because it can't be put into a box. But it is as subtle as a snake charmer and asks questions that it makes clear have no good answers.
It questions the nature of art and inspiration by looking at a famous art forger. What inspired Picasso and Matisse? Can you tell if you have a real one? Are you sure? If the fake is as inspiring as a work by the real master, is it still art? In a great twist, the main interviewer for much of the movie turns out to be the man who became famous for forging Howard Hughes' autobiography and making millions on it. That inspired the Richard Gere movie, The Hoax (2007). (I want to see that movie, mainly from seeing the real Clifford Irving in this film.)
This movie isn't a documentary, it is a film poem on the nature of reality. If that sounds like a joke, it is one of the many subtle ones Welles plays on the audience throughout this movie.