Automatic Data Processing ( ADP) said Chief Financial Officer Karen E. Dykstra has resigned to join Plainfield Asset Management, an investment adviser based in Greenwich, Conn. Dykstra's resignation is effective May 1. Afterward, she will help with the transition through June 30, the end of ADP's fiscal year, the Roseland, N.J., company said Tuesday. At Plainfield, she will serve as chief operating officer and chief financial officer of the firm's new direct lending and investment business. Until a successor is named, Dykstra's responsibilities will be divided between Dan Sheldon, ADP's corporate controller, and Raymond Colotti, the company's treasurer. ADP, a provider of payroll- and transaction-processing services, slipped 28 cents to $45.73.