BOSTON (Reuters) - William Ackman's Pershing Square Capital Management has sold its positions in Automatic Data Processing Inc ADP.O and United Technologies Corp UTX.N and built a new position in a company whose name has not been disclosed, a source familiar with the matter said on Monday.

FILE PHOTO: Bill Ackman, CEO of Pershing Square Capital, speaks at the Wall Street Journal Digital Conference in Laguna Beach, California, U.S., October 17, 2017. REUTERS/Mike Blake

Ackman announced the exit from ADP in a letter sent to clients and seen by Reuters on Monday and had earlier told analysts about the decision to sell out of United Technologies, the source said. A spokesman for Pershing Square declined to comment on either sale or disclose the name of the company in which the firm is building a position.

The announcements about ADP and United Tech are the most significant moves Ackman has unveiled this year and come at a time his firm is making waves with double-digit returns as Ackman himself stays largely out of the limelight.

At ADP Ackman said that investors earned a 51% return while his firm pocketed a $1.2 billion gain on an investment that started with a noisy fight two years ago when he tried to win board seats for himself and two associates.

Although he lost the fight, Ackman said his battle helped educate other investors and prompted management to make critical changes. He is leaving now, he wrote, because he expects future returns to be more modest now that the market is “more accurately pricing in ADP’s prospects for success.”

“If ADP meets its 2021 earnings targets, we estimate the stock will generate a low double-digit return from our exit price” of roughly $167 a share, Ackman wrote.

At United Technologies, Pershing Square likely made less money and has not given investors a full accounting of why and when the firm exited.

But the move followed Ackman’s push in June to get United Technologies to call off its planned merger with Raytheon. He told management he was “extremely concerned” about the merger which is slated to occur after United Technologies spins off its Carrier and Otis businesses next year.

Through July, Pershing Square Holdings, Ackman’s publicly traded portfolio, has gained 49.4%, compared with the average hedge fund’s return of roughly 5% during the same time.

The returns suggest that Ackman’s moves to rebuild his firm and reputation as a top activist after a string of losses are bearing fruit. In early 2018, Ackman vowed to focus more on investments instead of marketing and laid off staff and appointed deputies to field clients’ questions while he concentrated largely on investment research.

The last time he announced a new investment was in 2018 when he unveiled a bet on coffee chain Starbucks Corp SBUX.O, where he forecast the stock price could double over the next three years.