A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Start PowerPoint.
Choose File, Open and browse to the PPS/PPSX file you want to open.
It'll open as any normal PPT/PPTX would.
Save as either PPT/PPTX or PPS/PPSX, depending on what you want to have happen when someone doubleclicks the file in the future.