I am having trouble browsing PDF file and PDF based web site. What's up with this?

Currently, there is a known issue with PDF when you are using Webkit engine.

There are cases that browsing and scrolling some PDF files or PDF based web site using Webkit may cause Lunascape to crash.
This problem happens to be random and we found this problem happens in other Webkit based web browsers. That leads us to suspect there is some kind of incompatibility issue between AdobeReader and Webkit, and not bound to Lunascape. Meanwhile, there are no problem browsing or scrolling the PDF file/PDF based web site using other engines. When you encounter this issue, please switch rendering engine to either Trident or Gecko.