File extension used by Microsoft PowerPoint 2007. With Microsoft Office 2007, Microsoft introduced a new XML based file format called the Office Open XML (OOXML) document format. This new format is based on XML and has been adopted as an official standard for representing office documents like word processing files, spreadsheets, and presentations. These new files append an x to the end of the old Office file extensions, so PowerPoint files now have the .ppsm extension. We read and write this format natively, which is why we give you the opportunity to download, email, and share presentations as ppsm files.