Easier way to write on a pdf using the pencil tool?

I am a CPA and am paperless so I make a pdf of all of the tax documents and then check off what I've entered on the pdf using the pencil tool.  However, when I want to write a number or a quick notation, it is hard to write legibly with the mouse.  Is there a pen mouse or other way to be able to write more precisely on the pdf?  Preferably something wireless.