fair use does not say what kinds of publications are protected, open, or what have you. Fair use details a list of the "types of reasons" where fair use may apply. Those reasons could potentially apply to anything covered under copyright, regardless of the subject matter.
Playing games, however, is not an activity or reason given under fair use for which it is ok to use any elements of a copyright protected works.
However, I could see a case for a certain amount of latitude being provided for "commentary" and "review". There is nothing under copyright law which suggests the audience for either must include a minimum number of people. So one could, in theory, photo copy some charts and other information from a game tome and share it with their fellow gamers as part of a "review". Yeah, sounds fishy, but since that activity is never clearly defined, its open to interpretation. Which means, ultimately, its something that would be decided by a judge if it were brought into court. The judge would decide if your sharing of those certain elements would indeed be covered by fair use for the reasons given for the fair use. Obviously "to enjoy the game through the activity of gaming" would not qualify. No more than copying and distributing a movie is ok for "enjoying a movie".
So in short, sharing whole PDFs = copyright violation.
Sharing parts of the document for play = still copyright violation
Sharing part of it for review, commentary, etc, likely not copyright violation and it would be a "fair use" of the material. Doing it for gaming and claiming this in court *might* fly in court. But realistically speaking, it would also be an extremely rare publisher that would pursue such to court anyway.
Nothing in the vast, vast majority of gaming publications, is patented. So if you happened to "rewrite" the gist of what the publication was presenting, expressed in your own form, then its totally ok and not covered by copyright at all. So long as you also avoid those pesky trademarks in the process and hence be in trademark violation, this gets the job done. Its understandable that many folks wouldn't want to put the work in to rewrite the subject matter, and hence that is why the publication (print of PDF) has value and why copying it whole hog is illegal.
Ryan S. Johnson
Guild of Blades Retail Group -
http://www.guildofblades.com/retailgroup.php
Guild of Blades Publishing Group -
http://www.guildofblades.com
1483 Online -
http://www.1483online.com