You could just change the file attribute of whatever you want to protect to
"Read Only," after you copy it off your CD or wherever. That will prevent
overwriting the original file with a corrupted version.

Find the file(s) using WIN Explorer, right click on the filename(s), then
mark as read only.
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"Richard" wrote
I can trust mnyself, but if the original files were write protected when
the
came when downloaded, then it would be a safety measure from accidentally
altering the original files. I'm going to mess with the originals but save
the altered input files under a slightly different file name. I think I'm
making a perfectly valid point.