I think someone else pointed out that it's not possible to make a document
"non-alterable". You can read a TIFF file into Photoshop and edit it by
hand if you're determined, after all.
I've been searching for words to apply to .PDF and .EVY (Envoy) documents
to describe how they're different from usually editable (Word, ASCII text)
documents, but I've drawn a blank so far. I think what sets them apart is
that the information is not easily alterable, not that it *cannot* be
altered. I remember one of the major features of any security plan is a
deterrent, and that's just what this is. Editable or not, the perception of
GSTN f*x is that it's not editable, users are convinced that what they put
in one end will arrive at the other end.