Zathura is a simple, functional PDF viewer thats highly customizable, below are some common shortcuts / tips
a - page fit
s - fit width
r - rotate pages
d - side-by-side mode
Ctrl-r - Invert Colors
Tab - show index
f - follow links
along with above most of the vi's key bindings for movement / scrolling work, look at the Zathura man page for more keybindings
References