You hopefully have XP or later as it can't be (easily) done in earlier
versions also be aware that if people try to open this presentation with an
earlier version - it won't open at all.
Tools > Options > security tab add a modify password and save the
presentation.
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email john AT technologytrish.co.uk
Improve your skills -
http://www.technologytrish.co.uk/ppttipshome.html
Need a dice throw for a ppt game?-
http://www.technologytrish.co.uk/dice.html