Make the pies: Line 2 baking sheets with parchment paper. In a medium bowl, toss the blueberries, blackberries and raspberries with 1 1/2 tablespoons of the sugar and the cinnamon and salt. On a lightly floured work surface, roll out the puff pastry to 1/8 inch thick. Cut each pastry sheet into 4 squares and transfer them to the baking sheets. Spoon the berry filling over half of each pastry square, leaving a 1/2-inch border; fold the pastry over to create a triangle and press the edges together firmly to seal. Crimp the edges with a fork. Cut a small slit on the top of each pie. Refrigerate for at least 20 minutes.