Android
Foxit on Android asks for identity, wi-fi connection info, device ID, and call info, so that was a big 'ol bag of fuck-no. It also asks for in-app purchases.
Unfortunately I've got a motorcycle manual PDF that's a little malformed, so it causes lots of readers to crash. I need it on my phone because I refer to it about once a month for various obscure settings and when the bike emits error messages. Or I could just buy a Honda, I guess.
It's a landscape PDF and that seems to cause difficulties for lots of readers as well. Some crash when you rotate the device, just chop off major portions of the page, require you to scroll massively, or shrink it to unreadable postage-stamp size. This includes the Google PDF viewer.
Some of them slammed me with full-screen ads every couple pages. Seriously. [page][page][page]BUYDILDOSINCHINA[page][page]....
A lot had crappy UIs, with indecipherable icons, insane menu trees, or functions that just plain didn't seem to work.
As mentioned with Foxit, a lot wanted totally unrelated permissions.
I finally found "Document Viewer" 2.7.4 on F-Droid (search for "pdf") and it's also open-source under GPLv3. Crappy name. Good app. It has a quickly-clickable option to force landscape or portrait, as well as the ability to shrink-to-fit width/height/both/none like a desktop application can.