Good to know
What the viewer shows — and what it skips
A .pptx file is a zipped collection of XML files describing each slide, its layout and its media. The viewer reads that structure in your browser and draws every slide with HTML and SVG, so text stays sharp at any zoom level.
It is built for reading a deck, not presenting it: animations, transitions and embedded videos are not played. Speaker notes are not shown yet.
Old .ppt files (PowerPoint 97–2003) use a binary format that browsers cannot read. Open them in any presentation app and save as .pptx first.