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Imagine the following: You have two versions of a PDF, and want to know which of them is current, and what the differences are. Now, you could do the job manually, comparing page by page, running the risk that you might overlook something. If you have a full version of Adobe Acrobat, you can use the compare functionality built into it. There is another option though, and it’s free. It’s called DiffPDF. It does what you need it to – compares the PDFs and shows you the differences (or tells you that there are none) – simply, quickly, and for free. As in freedom, AND as in beer:
It’s available for download from RubyPDF Technologies.