Bill Ackman: ADP is not as efficient as it should be

Hedge fund activist Bill Ackman: We can increase margins at ADP by 60 percent

Bill Ackman: We're doing our best to reach out to individual ADP investors

Bill Ackman building stake in ADP

Bill Ackman sends new letter to ADP

Ackman: Likely will need new CEO of ADP

Bill Ackman announces major changes at Pershing Square

Pershing Square CEO Bill Ackman: The Fed will have to move early, can certainly do more than 3 cuts

Watch CNBC's full interview with Pershing Square Capital Management CEO Bill Ackman