Open refrigerated French bread and gently unroll at the seam, rolling dough out into a 10x13 inch rectangle.
For stromboli, layer dough with mozzarella cheese and pepperoni. Roll the dough up lengthwise as tightly as possible and pinch the edges to seal.
For calzones, cut dough into 4 equal rectangles, place the mozzarella cheese and pepperoni in equal portions on half of each square and fold dough in half over filling. Seal edges.
Place on an ungreased baking sheet (seam side down for Stromboli). Brush with melted butter and sprinkle with Parmesan cheese. Bake for 10-20 minutes (less time for calzones; should be golden brown).
Slice and serve with a small bowl of marinara sauce.