The 9/11 report is a US government work and therefore is uncopyrighted. It was born into the public domain and should remain there forever. You may deal in the document fully without any restriction due to copyright law.
Some bloggers (Techliberation.com, BoingBoing.net) noticed that the 9/11 report distributed from 9-11commission.gov has Digital Restrictions Management applied—copying a snippet of the report is disallowed in certain PDF readers (such as the Apple and Adobe proprietary PDF readers). Of course, you shouldn’t install proprietary software on your computer; you would use KPDF or some other free software PDF reader. KPDF lets you turn off the DRM in the application preferences, so you can read, print, and copy any part of any PDF document without hassle. It’s not hard to find or make an unencumbered copy of the report without DRM.
Whether the DRM can be circumvented (technically or legally) is a secondary issue here. DRM is inherently a bad idea and we don’t need it, corporate copyright holders have been arguing for it and are trying to convince you that you should want it too. Part of their argument tries to get you to see the world in the most restrictive way: any restriction we can technically impose on others is virtually self-justifying and hardly needs any debate. That state of affairs should not be seen as unavoidable, acceptable, or the default.