Melt the butter and squeeze in lemon juice and add crushed garlic. Lay 1 sheet of puff pastry in a large casserole dish.
Place the salmon fillet (skin side down) on pastry base. Brush the salmon with the melted butter. Place asparagus, artichoke hearts, and capers on top of the salmon. Cover the entire fillet and vegetables with a layer of puff pastry and seal the edges by pinching them closed.
Bake in the oven for 35 to 40 minutes in a preheated 350 degree oven, or until pastry is golden brown. Remove from the oven. Cut in portions and serve immediately.