Which PDF tool is the easiest to write scripts for?

I'm working on a project where I'm recording the mouse positions when someone is reading a pdf document. I tried Adobe because I heard it has a javascript console, but I had to pay for the professional edition. I tried pdf.js (which reads the pdf and renders it as a canvas in a browser) b开发者_StackOverflowut it doesn't align characters properly, which defeats the purpose.

So I was wondering, are there any good pdf readers, stand alone applications or browser plug ins, that will let me add scripts onto them?