ViewPDF shows PDF files, clearly indicating annotations and possible mistakes (such as spelling errors).
ViewPDF is licensed under the GNU General Public License v 2 open source license.
To build ViewPDF you will need a good C++ compiler (e.g., GCC), the Qt 4 libraries (at least Qt 4.6), the Poppler library (at least 0.18, although at least 0.20.4 is recommended), the enchant library, a spelling library for enchant to use, and at least one spelling dictionary—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 viewpdf-0.6.2.tar.gz (19K; SHA1: b157da0f145119f1392c97273e097742bd00d0ee). Building follows the standard pattern for Qt 4 applications and is explained in the README; the steps are reproduced here:
If you like ViewPDF, you might like to buy one of my books. I also provide training and consultancy in C++, Qt, Python, and PyQt.