This is a handy-dandy little trick I stumbled upon purely by accident and hope it helps some of you out there dealing with PowerPoint files.
Some PowerPoint files that you receive come with the extension ".ppsx". This means the file is a "slideshow" and you cannot get at the underlying data in the individual slides. The file name looks like this:
To open this file as a normal PowerPoint file, simply change the extension from ".ppsx" to ".ppt", and you can open and edit the slides to your heart's content!
Such a simple trick. And, you can mess with people that send out "protected" .ppsx files next time you get one!