Ghostscript

Merge PDF's

merge 2 ore more pdf's together to one multipage pdf...

gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE="merged_file.pdf" -dBATCH file1.pdf file2.pdf file3.pdf ...

Split PDF's

(Not ghostscript)

get page-subsets out of PDF's:

convert file1.pdf[0] file2.pdf[0-1,3] output.pdf

Strip down size/quality

reduce size of PDF-files

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

-dPDFSETTINGS=/screen   --> low quality
-dPDFSETTINGS=/ebook    --> medium quality
-dPDFSETTINGS=/prepress --> full quality