Maybe an unlicensed pornographic film? Double points if Clark doesn't find out about it until someone he knows references having seen it? Poor Clark. No one would have suspect that Supes had a secret identity to write that one. They could even use an "of Steel" title, but might have to change that first word.
The problem with a serious movie (if written by a 1990s person, and not Utopian) is that I'm not sure what it would be about. I'm so familiar with Clark existing, I have trouble coming up with a story where there is no secret identity. Maybe a docudrama about some of the things that Superman has done? But then he'd have to be interviewed, and he'd end up lying about some of the details (or protect his secret identity), and I'm not sure how Clark would feel about that.
