Pershing Square, the investment fund run by famed investor Bill Ackman, has filed for an IPO, it announced on Tuesday. Ackman's fund is planning a dual listing of Pershing Square and a closed-end investment company, Pershing Square USA, on the New York Stock Exchange. The company is seeking to raise at least $5 billion in the IPO, it said in a statement announcing the planned listing. "Shares are being offered at a price of $50.00 per PSUS Share and investors in the PSUS IPO will receive, for