This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
I wouldn't call the third document the "difference" of the first two. I'm not exactly sure how you would display the difference, but that isn't it. It's more like the union of the two documents. So you might want to clarify your requirements before looking for implementations of those requirements.