Link to related application on Play Store: https://play.google.com/store/apps/details?id=org.sufficientlysecure.viewer
Play Store version is stuck at 2.7.9, but up to 2.8.1 can be downloaded from other sources like F-Droid.
GitHub page: https://github.com/SufficientlySecure/document-viewer
I've been a user of this application for years. It's a really good document viewer, and probably the best for quick and neat PDF handling as far as my wisdom and experience goes. However, since I upgraded to Oreo (8.1) the last couple years the app has had instability problems. This has come to an end because user hwasiti from GitHub reported he had found a fix to the issue around a couple weeks ago in a bug report thread of mine.
Just remembered. I'm posting this here in case this is of help to someone in this large community.
Have fun.
