Preheat oven to 400 degrees F. Unfold puff pastry on a parchment-lined baking pan. With a knife, score a 3/4-inch border around pastry. Transfer to oven and bake until puffed and golden, about 15 minutes. Using parchment, transfer pastry to a wire rack to cool completely, about 15 minutes.
In a medium bowl, using an electric mixer set on medium speed, beat cream and sugar together until stiff peaks form. Spread whipped cream on pastry in an even layer, up to scored border. Dot with berries.