Preheat the oven to 350 degrees F. Season the entire duck with salt and pepper. Place the duck on a roasting pan and roast for 2 hours. In a mixing bowl, whisk the flour, eggs, and water together. Whisk until smooth. Season the batter with salt. Oil a 6-inch diameter non-stick pan. Heat the pan over low heat. Pour 1 tablespoon of the batter into the pan. Let spread over the surface of the pan to form a very thin pancake. Cook until the pancake is set on top and cooked underneath, about 30 seconds. Flip the pancake over and continue to cook for 30 seconds. Pile the cakes on top of each other and cover with a damp towel to keep them moist. Repeat the above process until all of the batter is used. Remove the duck from the oven and remove the wings and legs. Carve the remaining meat into thin slices, reserving the skin. To assemble, smear each pancake with the Hoisin sauce. Lay the duck slices and crispy skin in the center of each pancake. Roll the pancakes, tucking the ends in, like an egg roll/envelope. Garnish each plate with either a leg or wing.