Open PowerPoint, then click File > Open. Look for the pps file you want and
click open. From there, you can edit the slides. It might also be password
protected from modification.
In both cases, you will have to seek permission from the owner.
--
Shawn Toh (tohlz)
Microsoft MVP PowerPoint
(Amazing PowerPoint animations, artworks, games here)
http://pptheaven.mvps.org
PowerPoint Heaven - The Power to Animate
