Don't be too sure about ASCII text file either, it may still contain a bit of metadata like the BOM (although then technically it's not pure ASCII, but rather UTF, but still it means you have to check the encoding used by your favourite text editor).
In case of UTF8, BOM isn't information at all, it's always the same 3 bytes (endianness mark is meaningless on byte-based encoding). And being added by default Windows plain text editor, it's fingerprinting usefulness is rather limited.
