PDF readers for Nokia are fully functional, but...
I don't feel very comfortable using them. It is necessary to zoom the page and then browse around it. So, it is possible to retrieve information by spending huge amount of time moving back and forth on the same page. Not very productive.
I used Palm 3C before. Adobe made converter for Palm, so that it was possible to browse PDF file almost the same way as it is done in FBReader. Text was converted to reasonable size and pictures were kept small. Formatting was different than in original document, but it was readable. When you want to see detailed picture, just click on it and it is magnified. It was very functional even on 160x160px screen. Something similar was done for pocket PC.
Have anybody heard about this kind of converter, so that it would be possible to enjoy viewing PDF files on Nokia. I would not mind if this would require preliminary conversion on PC.