Is it possible?? I got the Penumbra Collection from a retail store awhile ago & would like to add it to my Steam account but it didn't come with a CD key or anything...
The Penumbra Collection is not on the accepted retail CD keys list: https://support.steampowered.com/kb_arti...-wusf-3601 so even if your product came with a CD key, you would not be able to activate it on Steam. However, the Penumbra collection is currently $5 for the Halloween weekend sale on Steam.