Submit portable freeware that you find here. It helps if you include information like description, extraction instruction, Unicode support, whether it writes to the registry, and so on.
DiffPDF can compare two PDF files. It offers three comparison modes: Words, Characters, and Appearance.
By default the comparison is of the words on each pair of pages, but comparing character by character is also supported (e.g., for logographic languages). And there's also support for comparing the pages by appearance (for example, if a diagram is changed or if a paragraph is reformatted, or a font changed). It is also possible to compare particular pages or page ranges. For example, if there are two versions of a PDF file, one with pages 1-12 and the other with pages 1-13 because of an extra page having been added as page 4, they can be compared by specifying two page ranges, 1-12 for the first and 1-3, 5-13 for the second. This will make DiffPDF compare pages in the pairs (1, 1), (2, 2), (3, 3), (4, 5), (5, 6), and so on, to (12, 13).
DiffPDF is licensed under the GNU General Public License v 2 open source license.
I finally had occasion to test this and found an important limitation: the program requires a 1 to 1 relationship between your PDF files. Meaning for example if you have two exactly the same 10 page documents save for a blank page inserted before page 2, the rest of the documents will come up as different. The program isn't smart enough to notice that the data has just moved down slightly.
That said, I preferred it in some ways over Acrobat Pro 9's comparison tool, who's output wasn't terribly easy to understand.
The portableapps version works well for me for some documents I had to compare, but of course YMMV as they say.
Just to note there is also a command line solution, https://vslavik.github.io/diff-pdf/ (mac, linux, windows) but for some documents the files are significantly larger. I'll post a note in the CLI section for cross reference.