I own Shadowrun Returns on steam but if I am to buy the dlc here on gog will it work with the steam version or only with the gog release?
I apologise if this is a stupid question but I´m unsure.

Thanks.

non, ça ne fonctionnera pas.

You're better off asking customer support. I'm betting no because the portable content packs are installed placing a folder on the installation folder, and the GOG version of Dragonfall is an installer, not a zipped folder. However, taking the folder from one Shadowrun Returns installation to another should probably work, because the files must be the same on both.

Finally, this doesn't seem like a good idea.