Postscript files (.ps) are usual and in many cases some manipulation is needed. [for more see also here]
Convert from a ps to pdf file:
$ ps2pdf input_file.ps output_file.ps
Merge 2 or more files:
$ psmerge -ooutput_file.ps input_file_1.ps input_file_2.ps [more_files]
note: that -o and output_file’s name are not separated by any space
Put more pages per page:
$ psnup [options] -n input_file.ps output_file.ps
[options]: -l , -r which “corrects” for orientation
-n: number of pages from input_file.ps that will be on a single page of output_file.ps (for example -2 for 2 pages/new page, -4 for 4, etc.)