Generally only from your backup copy. Once you save a file, it turns off
the Undo for previous actions. You may very well have to recreate the
slide.
I would not hold out any promise for trying what a few on this and other NGs
have said about trying an unerase program to "recover" the file previous to
the save. I have never had any luck recovering Saved files with this method
but it may work for you.
