Using HTML for that purpose, emedding large images and other multimedia files in it, while in theory could work, is another nightmarish stretch of the standard

Using HTML for that purpose, emedding large images and other multimedia files in it, while in theory could work, is another nightmarish stretch of the standard and depending on the size of your document could bring your system to a stall. PPTX is Microsoft open-ish format for presenting slides and I doubt using it for that purpose would be a good idea.