On a lightly floured surface, roll each pastry sheet into a 12x10-in. rectangle. Cut each sheet into four 6x5-in. rectangles. Place a salmon fillet in the center of four rectangles.
In a small bowl, combine the scallops, cream, onions, parsley, dill, salt and pepper. In another bowl, beat egg white on medium speed until soft peaks form; fold into scallop mixture. Spoon about 1/2 cup over each salmon fillet.
Top each with a pastry rectangle and crimp to seal. With a small sharp knife, cut several slits in the top. Place in a greased 15x10x1-in. baking pan; brush with egg. Bake at 400° for 20-25 minutes or until a thermometer reads 160°.