What’s the difference between a PowerPoint .ppt file and a .pps file? Well, duh! One ends with an “S” and the other ends with a “T”. Really! No kidding! That’s it. Otherwise, they’re identical files.
A .pps is just a .ppt file with a different file extension that tells PowerPoint to open the presentation directly in slide show view, allowing the viewer to skip the Normal (editing) view.
If you open a .ppt file you’ll see it in the Normal, editing view.
If you open a .pps file you’ll skip directly to the slide show
You might want to consider sending a .PPS file instead of a .PPT file when you just want people to view the slide show the way you intended it to be seen instead of having to fumble around in PowerPoint and maybe never seeing it as an actual slide show.
To “convert” from one type to the other all you have to do is rename the files and change the “s” to a “t” or vice versa. (You can also use the File » Save As… menu in PowerPoint.)
The file types for PowerPoint 2007/2010 are .PPTX & .PPSX , but the trick of simply renaming the file with a different extension doesn’t work for them. Now you have to use PowerPoint’s File » Save As… menu to save in the type of file you want. (Presentation or Show).