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zathura evince okular pdfjs
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.