GitHub · Google Play
Opens PDF, Word, Excel, PowerPoint, photos, video, audio, Markdown and code, all rendered on the device. About 5 MB, one build for every processor, Android 8.0 and up.
Search works in every document type. PDF text selects, copies and reads aloud to a screen reader, and there is a night mode that turns the paper black and leaves most photographs alone.
Its permissions page is empty and the manifest has no INTERNET so it can't open a network connection. Files reach it through the system picker, an Open-with intent, or a folder you grant once. The About screen asks Android what the app requests and shows you the result.
Not an editor. Legacy .ppt does not open. Complex PowerPoint renders approximately.
I will be in the comments today, so ask away, including why it isn't on F-Droid yet.