I recently wanted to send something to someone
relating to a
 non-computer related project I'm working on, and due to what it is, I
 don't want anyone being able to modify the file, but I don't mind
 them printing it out, I was able to do this with PDF. 
Sorry to burst your bubble, but you weren't.  All you were able to do
is make it a bit harder.  (If it can be printed, it can be captured and
modified - at least until they get DRM pushed into printers, and given
the installed base, that won't be a for a while yet.)
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