Bill Ackman’s Pershing Square, the largest shareholder of General Growth Properties Inc (NYSE:GGP) has just filed a 13D with the Securities and Exchange Commission (SEC), requesting that the company put itself up for sale. Ackman writes several pages explaining his background helping the company re-organize out of bankruptcy. Ackman’s best investment so far has been his purchase of General Growth Properties, which he bought at approximately $0.37, which Ackman notes is a 77x return on the investment. Shares of the company are currently trading at $19.10, up 3.3% for the day. Ackman notes that he owns 72,233,712 common shares of General Growth…