comparepdf is a command line tool for comparing two PDF files. By default it compares their texts but it can also compare them visually (e.g., to detect changes in diagrams, images, fonts, and layout). It should prove useful for automated testing.
If you want a GUI application that shows the detailed differences between PDFs use DiffPDF instead.
comparepdf is licensed under the GNU General Public License v 2 open source license. To build it you will need a modern C++ compiler, the Qt 4 libraries (at least Qt 4.4; 4.6 or later recommended), and the Poppler library (version 0.14.0 or later)—all these should be available as standard packages on most Linux and BSD systems. For Mac OS X you'll need to install Xcode for the compiler and then get Qt and Poppler separately. The source is comparepdf-1.0.1.tar.gz (15K; SHA1: 01774dac78dca9b712d55bfdbaf58c4b0bd31295). Building follows the standard pattern for Qt 4 applications and is explained in the README.
Steven Lee has built a version for Windows. It is available from his blog http://soft.rubypdf.com/software/diffpdf/comparepdf-windows-static-version or from here comparepdf-1.0.0-win32-static.zip (4.6MB; SHA1: 8f1db5334a175502691570c89dbb4c580c6fa9ea).
If you like comparepdf, you might like to buy one of my books. I also provide training and consultancy in C++, Qt, Python, and PyQt.