https://sureai.net/forum/viewtopic.php?t=3144
· Steam is a little rigid concerning its copy protection. Unfortunately, due to that feature you
can't have Nehrim and Oblivion installed separately, so you will have to overwrite Oblivion
with your Nehrim installation.
· First create a copy of your Oblivion folder as a backup. You can find this in the folder
Steam/SteamApps/common.
· Now you can execute the Nehrim installer, choosing any place on your harddrive for
installation.