Scrolling a Document

Question

Hi,
I'm working on an applications which reads a pdf document. As we all know we have hand tool in most of the pdf reader, which is used to scroll the document. My issue is when I use the hand tool to scroll the mouse, the speed of the movement of the mouse and the speed of the scrolling of the document is not synchronized. Not matter how fast or slow I move the mouse, speed of scrolling of the document remains same.
I need help in developing the logic for this.
Thank you,