Any PDF reader for my unlocked 3GS running iOS 4.2.1 ???

[Qxx1]

I need a PDF reader and there are plenty of those on Appstore but i cannot run most of them since my iOS is really old (4.2.1) and currently i cannot upgrade to any UNTETHERED iOS.
I downloaded a few but hey were not able to detect any pdf files in the phone (but itunes shows pdf files under my iphone`s books tab)
so any apps for me??