Preheat oven to 350 degrees F (175 degrees C). Line a 9x13-inch baking pan with parchment paper.
Mix pumpkin puree, evaporated milk, 1 cup sugar, eggs, and cinnamon together in a bowl; pour into the prepared baking pan. Sprinkle cake mix over pumpkin mixture and top with pecans. Drizzle butter over pecan layer.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 1 hour. Cool cake in the pan, at least 30 minutes. Invert cake onto a flat plate.
Mix whipped topping, cream cheese, and 1 cup white sugar together in a bowl; spread over the cake. Chill in the refrigerator, 1 to 2 hours. Cut into 1-inch squares.