Enter Sneak mode, then sneak up behind the enemy you wish to kill. Do not let him see or detect you. You must be some distance away. While in Sneak mode, take out your bow and launch an arrow at the target. When the arrow is in mid-flight, immediately enter your inventory and equip any bladed weapon. Notice that the damage of the blade is added to your sneak (in this case, arrow) damage. You must be at a far enough distance to have time to enter your inventory and equip a bladed weapon while the arrow is in mid-flight.