print 4 pdf pages in one page

* sudo apt-get install texlive-extra-utils
* pdfjam /tmp/590b471deec652.86443293.pdf /tmp/590c1db0a68a73.01507640.pdf /tmp/590c1e3167e5e3.20721152.pdf /tmp/590c1efda5cc54.43315336.pdf --nup 2x2 --outfile /tmp/out.pdf