It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

What is it? I have no clue. I have the game, the enhanced version, and the attic dlc, but this is there too.
A little late to the party, but I don't think this is the complete game. There is a steam entry with identical content, but slightly different name, that is marked as DLC:
What the original poster meant was that they own the digital deluxe edition. That consists of the game, the nome dlc, the soundtrack, art book, wallpapers, etc. However, in the offline installer files, there is a dlc simply labelled as DLC bonus bundle. It's a .exe file at around 6MB in size. Obviously it contains no content and is simply an unlock of sorts. The thing is, the nome dlc is there as well, along with all the bonus extra files. So..........this file does what exactly? It seems like a useless file.