To redeem a BoxOff Store code for an extra manual or other content, you need to:
1 - go to boxoffstore.com
2 - click on "Login" in the upper-right corner
3 - If you do not have a BoxOff Store account yet, you are going to have to create one -> Select "Register"
4 - fill in the form
5 - activate your newly-registered account by clicking on a confirmation link we have sent to your e-mail addresses provided in the above form when signing up.
If you do not see an activation mail from us, check your SPAM folder, please. If it is missing there as well, send a message to firstname.lastname@example.org to activate your account.
6 - having signed into your newly-created account, select the "Got code?" option in the upper-right corner
7 - enter your BoxOff Store code (not Steam code) here
8 - next, select "Redeem"
9 - you can access downloadable content under the "Your collection" tab, having signed in to your account.
10 - please remember that it is not possible to transfer content between different accounts at BoxOff Store, so you will need to sign in to the appropriate account before downloading your content.