You can but I don't recommend it. Many recipes call for using one but I am a bit old-fashioned when it comes to pie crust and really find a pastry cutter or two forks the best method. It's the best way to end up with a variety of different sizes of butter throughout the pie crust. The food processor can sometimes create butter pieces that are too small which means your crust may not be as flaky.  I can’t imagine what my big mama would think if I pulled out a food processor for pie dough.  I love a little bit of hustle in the kitchen.  It makes me feel like I am doing something.