If I buy a key from a 3rd party site...can I access the DLC on steam?

[UnderWorldPapi]

Hello, I want to buy some DLC for the game. Sites like greenmangaming says you have to redeem the key through ZeniMax. Does that mean redeem through the launcher or no ?. Can I still play or access the DLC on the Steam copy? ( I play through steam )

[Stoltverd]

Nope. You'll have to buy it again if you want the steam version.
Alternatively, you can add it as a non steam game if you only want the overlay

[MorningStar]

Yes. If your Steam and Zenimax account are linked you can enter the code in the main site. It won't show on Steam as being purchased but you should be able to play that dlc. Check the crown stores purchased dlcs ,they should be there as being bought