The Undo function is only activated when you used an edit function on the
current presentation that can be undone. First thing to do is to go to Tools >
Options > Edit and set the maximum number of undos to a non-zero number. Keep
the number to something practical and reasonable, since the function uses system
resources and can impact PowerPoint performance. Then experiment. Add a text
box to a slide and type a word. Then press Ctrl + Z.
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Sonia Coleman
Microsoft PowerPoint MVP Team
Autorun Software, Templates and Tutorials
http://www.soniacoleman.com