Recently I installed Ubuntu Oneiric Ocelot 11.10 on my desktop. It has a built-in PDF reader which I accidentally uninstalled when I removed ghostscript with the following command:
sudo apt-get remove ghostscript
I have no clue what the name of the PDF reader was, and how to get it back on board. Seems like a really easy question, but couldn't figure it out with Googling only.