Manipulate pdf files with Ghostscript

Crop

This may be useful when the margins of the pdf files are too large, e.g. for printing or displaying in a tablet device. See this post.

Merge

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=finished.pdffile1.pdf file2.pdf

-dBATCH: exit after last file, otherwise GhostScript will keep running. -dNOPUASE: no pause after each page, otherwise GhostScript will pause for user interaction after each page. -q: quiet, fewer messages.

Split

Change page size

gs -sDEVICE=pdfwrite -dDEVICEWIDTHPOINTS=595 -dDEVICEHEIGHTPOINTS=842 -dPDFFitPage -o output.pdf input.pdf 

595×842 is the standard A4 size.