If there’s no source directory then it sounds like you’ve downloaded a retail cooked version of a game which is freely available if you buy it on Steam. Stop wasting your time trying to open the project.
Whilst it may be be possible to open the art assets, I don’t think you’re going to find any help here, I’m afraid. A lot of the people that answer posts in these forums work for a living making games; it’s not really the place to post links to pirate video games, is it?