A PPSX file is a slide show created by Microsoft PowerPoint or another presentation program, such as OpenOffice Impress or SoftOffice Presentations. It contains a finished collection of slides that are used for slide show playback.
PPSX file open in Microsoft PowerPoint 2016
Once saved, PPSX files cannot be edited and may only be viewed. Therefore, they are useful for sending finished presentations to users that just need to view the presentation instead of editing it.
PPSX files are saved in the Open XML format, which was introduced in Microsoft Office 2007. They may be opened by PowerPoint 2007 or later, or by earlier versions of PowerPoint with the Open XML component installed.
NOTE: Even though OpenOffice.org does not natively open PPSX files, you can still open them in the software by selecting the "Microsoft PowerPoint 2007 XML" option from the list of supported file formats.