Heard of Adobe Reader? If not, you must be coming out from don't know which jungle, just like Karen.
If you like Adobe Reader, you will love Foxit. I prefer Foxit as it load PDF documents much faster. No delay in scroll between pages & does not takes up a lot of CPU processing power. It takes less than only 4MB of hard disk space to install.
I'm glad I switched to Foxit.
Download it here.