Hello! If you bought the DLC here, you should be able to add it directly to the Steam version without having to buy it again. Simply download the file (it should say "dlc_wedding.rpa") and place it in the "game" folder in the Steam directory for the game. You can find that by right clicking on the game in your Steam library, going to "Manage", then "Browse Local Files". And that should work! If you need more help, just let me know.