Thank you for that! It looks like that is what the file is supposed to be. If you put that directly into the "game" folder of the larger game directory, that will give you access to the DLC! It's a .rpa file, so it should work just fine. If you have any other trouble, though, let us know. And thanks for playing!
It looks like you're missing a file, so you might want to try a clean reinstall. Simply delete that current version of the game, and download it fresh here from itch.io. Make sure you set aside the "dlc_wedding" file before you do. Check that the reinstall has the "archive.rpa" file in the "game" folder, then try it again. Hopefully that works!