Pdf

Viewers

zathura	customizable vim-inspired pdf viewer
evince	lightweight pdf viewer
okular	heavyweight pdf viewer, supports encrypted docs, signatures
pdf.js	javascript viewer, embedded in several web browsers

Encoding and Manipulation

ghostscript		CLI utility for ps/pdf manipulation
pypdf		python module for pdf authoring/manipulation

File Format

PDFs are composed of boxes, ....

Boxes

mediabox		The largest dimension - contains all crop-marks etc for printing.
cropbox		Where the page should be clipped (in pdf viewer/when printed)
bleedbox		Where the printed material should be clipped (generally slightly larger than cropbox for print)
trimbox		The actual width/height
artbox		seldom used, allows you to crop small componenents from a pdf for printing.