Can you have the product key for fsx

Answer: The only legal way of obtaining a Product Key for Flight Simulator X is buying it in a store. Each individual box of FSX comes along with it's own Product Key.
If you attempted to enter a product key from another box, FSX would not install. This is because the Product Key numbers themselves are within the installation program on the CD's. (It's Microsoft's way to prevent illegal pirating & copying)