Yes, since all those who are baptized into Christ from one communion and are united with one another, the living can also help the souls of the faithful departed in purgatory. [1032, 1414]
When a man is dead, he can do nothing more for himself. The time of active probation is past. But we can do something for the faithful departed in purgatory. Our love extends into the afterlife. Through our fasting, prayers, and good works, but especially through the celebration of Holy -> EUCHARIST, we can obtain grace for the departed.