Lovejoy (1986)

Sam Wendell, an old forger, dies of a heart attack while being pursued by a mysterious priest, leaving behind one of his small forgeries. Sam had told his wife it was the key to a fortune, and the priest soon tries to break into the Wendell house. Lovejoy aims to unravel the puzzle, by way of helping Sam's widow (who's left with very little) to recover anything of value. Along the way, Lovejoy dresses up as a priest.