Ed wrote:

I have several sheets of old Plexiglass from which I can't remove the
paper backing. The adhesive apparently is dried out. I tried a heat gun
but that didn't help soften it. The clear film on the front side comes
off fine. Anybody have any ideas? Thanks.

Chem-peel - Specifically designed for that purpose and works very well
without harming the plex. I got mine from a plastic supply house,
imagine you'd have to do the same as it was clearly not a consumer
product. Seem to recall it was made by something like "Ogden Labs" in
Utah.

Pete C.