Reposting from reddit, the app is a recent addition to the Fossify roster and already a quite good PDF/document viewer.

Fossify Documents has been updated to v1.1.0. This update comes with the following new features:

• Select and copy text from PDFs

• Search within PDF, DOCX, and HTML files

• Dark PDF pages

• Option for horizontal PDF scrolling

• PDF table-of-contents navigation

• An option to hide floating page numbers

It also fixes files opened from other apps missing from Recents and problems editing externally opened CSV files.

• F-Droid: https://f-droid.org/packages/org.fossify.documents/

• GitHub: https://github.com/FossifyOrg/Documents/releases

• Google Play: https://play.google.com/store/apps/details?id=org.fossify.documents

If you don't see the latest version on F-Droid, please use the IzzyOnDroid repo or the GitHub releases.