think you are in trouble ;o)
Hi,
I don't think that there is a easy way to implement what you want.
files are basically files for the filesystem of your OS. There are no special filetypes that can be used for your purpose... just files.
So what ? why shouldn't someone try to open your files with a wrong application ?
you know the effect if you try to open a binary (exe etc.) file with an ASCII-Editor ? yess only crappy chars that are of no use.
so if you encrypt your files with a simple mechanism it will be very, very hard for someone to get a bit of structured information.
Greets
Juergen