Thaw duck if frozen, drain well.
Make the garlic and herb butter by mixing softened butter with garlic and rosemary.
Pat dry with paper towels on the inside and outside. Place on a rimmed baking sheet.
Carefully make an X in just the skin of the back of the duck. This will help the fat to drain as it cooks.
Flip the duck over and loosen the skin over the breast and spoon butter mixture under the skin.
Truss the duck with butcher twine.
Place the duck on a wire rack and place over a foil roasting pan.
Spray with olive oil and sprinkle with salt, pepper and smoked paprika.
Prepare a grill fire to 350°.
Cook the duck over indirect fire with the lid closed.
Keep the grill fire between 325° and 350°, cook for about 1 hour until duck reaches 165° using a digital meat thermometer. Test in the thick part of the thigh near the bone. Do not overcook the duck or it will be dry and flavorless.
Remove duck from the grill and allow to rest over the roasting pan for 15 minutes.
Drain juices into the roasting pan.
Move duck to a cutting board to carve.
Prepare the orange sauce by adding orange marmalade to a small sauce pan with orange juice, garlic, ginger, salt and pepper. Whisk to combine. Place over medium heat, cook 2 minutes. Stir in brown sugar and continue to cook until sauce starts to bubble. Remove from heat.
Serve orange sauce with grilled duck.