Recently, the PDFreaders.org team has removed a PDF reader called SumatraPDF from the list of free PDF readers due to presence of non-free code in the software. We were notified of the problem by a community member and have attempted to resolve this with the developer. Unfortunately, they have not been receptive to our arguments, and hence we have been forced to take this action. My only regret is that we have taken far longer to implement this action than I would have liked, and for this I would like to ask our users’ forgiveness.
The reason why we cannot consider SumatraPDF to be Free Software is its use of the unrar utility that places restrictions on the purpose the utility may be used for (licence). Freedom 0 is the freedom to run the software for any purpose; it is obvious that parts of SumatraPDF may not be used to recreate a certain compression algorithm. This is a usage based restriction; ergo, SumatraPDF cannot be considered Free Software.
The situation with SumatraPDF is especially unfortunate as the unsuspecting user who, believing all dependencies to be GPL-compatible, unwittingly recreates the compression algorithm or creates a WinRAR-compatible archiver may be exposed to legal liability. I hope that SumatraPDF will choose to make use of a free decompression library that supports RAR archives; however, while they continue to make use of the non-free library, SumatraPDF cannot be recognised as Free Software.