Funny since the PDF you linked to mentions "The Face Book". Page 11 under the "Entire Agreement" Section
Yes, I know the PDF I liked to includes that. My point is that FB doesn't think that's actually the agreement that Zuckerberg signed. Let's pose a hypothetical situation:
Ceglia posts an ad on craigslist asking for programming help on a new startup called StreetFax. Zuckerberg responds, and they work out a contract that looks similar to the one that was in the filing, except there was never any mention of "The Face Book", "The Page Book" or anything *other* than the StreetFax stuff. They both sign it, Zuckerberg gets his money, Ceglia gets the StreetFax stuff, and then they part ways sometime in 2003 and never speak again.
Fast forward to June of 2010, and suddenly Ceglia is providing a poor quality copy of a contract that looks similar to the one Zuckerberg had signed 7 years ago, but now includes stuff about Face Book that was never on the original contract, and is claiming majority ownership of a billion-dollar company as a result of it.
Now, it may be that the contract in the filing is the actual contract between Zuckerberg and Ceglia, but I find it equally plausible that the contract is a forgery. Zuckerberg's faults have been highlighted here on numerous occasions, and Ceglia apparently was under investigation for alleged fraud with an unrelated business of his. I'm not sure who to believe, but the details of the case that have been made public makes it obvious that no one other than Ceglia and Zuckerberg probably know the truth, and neither has been able to make a convincing case thus far. I will grant that at this point Ceglia obviously has made a more convincing case than Facebook/Zuckerberg, but I'm sure that neither has tipped their entire hand at this point. The fact that Facebook is also going after other avenues (e.g. arguing that even if the contract was the one they both signed, that it isn't valid or the statute of limitations is up, etc.) makes me think that they don't have good evidence that the contract in the filing is a forgery, even if that is what they believe.