PDF

Firefox
Firefox browser can open PDF files.

MuPDF
A lightweight PDF viewer. Install package. When the file manager asks for a program to open the PDF file, navigate to. Handling happens mainly by keyboard, see e.g. debian manpage.

Xpdf
An X11 PDF viewer (website). Looks a bit old-school (screenshot).

zathura
A minimalistic, vim-like document viewer. Handling by keyboard, see manpage.

CorePDF
Part of CoreApps collection. Depends on.

Atril
MATE document viewer. Depends on file manager, itself depending on.

Evince
GNOME document viewer. Depends on, these are just the core libraries (not the full desktop).

Okular
Document viewer of KDE. Depends among others on  and.

qpdfview
Lightweight PDF viewer for Qt. Not available on Alpine Linux and postmarketOS. For compliling: source on Launchpad.

Pidif
Lightweight PDF viewer using GTK4, built especially for small touch screens. Available on Alpine Linux and postmarketOS as.