Pershing Square’s Bill Ackman tells CNBC he bought more ADP shares on Friday.

I am “still buying the stock as of this morning,” Ackman said in an exclusive interview with CNBC’s Scott Wapner on “Halftime Report” Friday.

Ackman said he seeks “transformational change” at ADP and thinks its profit margin can “expand by more than 50 percent.”

ADP released details on the fight brewing between the Pershing Square Capital Management manager and the payroll processor. ADP confirmed Pershing had amassed an 8 percent stake through Friday morning and that the manager wanted to oust the chief executive.

Word that Pershing Square was building a position in the company sent the shares up more than 10 percent late last month. Pershing previously owned ADP shares from 2009 to 2011.

— CNBC’s Scott Wapner contributed to this story.