So I downloaded all the offline backup installers from the games I have purchased on GOG just incase I ever lost connection etc.

One of the games I want to play now but I also want to get the achievements through GOG Galaxy.

I guess my question is in order to do that do I need to install/copy the game a second time onto my PC?
Hope that makes sense. Thanks.

No, just install Galaxy and import the game folder.

Nope, as Randalator said, you can just import the folders. There's also an option to have Galaxy scan for GOG games under the "Add games & friends" menu in the options.

I tried the scan Gog for games option and selected the game folder and I got a prompt saying no games found.

Add game manually takes me to the game page on Galaxy with the option to install. But I already downloaded the offline backup installer for the game.

Also I havent actually installed the game from the offline backup. I just downloaded those to store/save. Maybe thats the problem I need to install first from the offline backup then find the game through GOG Galaxy?

Oh yes, if you download the offline installers, you definitely want to install the game via them first and then you can link it into Galaxy. :)

Oof

Thanks. That helped me too.

Thanks everybody it worked!

I'm glad everyone was able to get it figured out!