If I do a find for 'Containing text' in the Find panel, Opus will search inside Word Documents, but won't search inside Powerpoint documents.
I tried adding .pptx to the list of zip files and enabling 'Search inside archives', but the operation then returns a list of individual xml files from inside the pptx file instead of a reference to the pptx file itself.
Both come from Microsoft and I've only found them via searching, so there may be newer/better versions out there, or possibly an optional component that is built into your Office install.