Is this possible at all? In the gog instructions there is written that I should go to LIBRARY and that there is an INSTALL option. I see no such option there at all. I bought my game in a regular store. Do I need to buy it from GoG to be able to play it through gog?

Seriously?

To install a game from a CD, one usually just has to put the CD into the drive and it should autostart the installation. If it doesn't autostart, open the Explorer, go to the CD menu and doubelclick on the autostart- or installation-file.

Gog's instructions are only for the games sold from gog.com.

Damn it, that's not what I mean. Darkest Dungeon requires activation and access to the steam platform. The access to which I cannot get because no safeguard confirmation e-mails are sent to me. I want to play through GOG. How to do it? Can I play my Darkest Dungeon (bought in the regular store) through GOG instead of playing it through steam? How to do it?

I see. Darkest Dungeon is cheap now. I'll try buing it from GOG.

Hopefully the retail game came with some physical extras so that it wasn't a complete waste of money.

That is why I don't buy physical games anymore... More often it's just a Steam installer with a code.

Oh, does it mean that I still need Steam to play Darkest Dungeon on GoG?

If you buy it from GOG, then no. GOG sells the GOG version of the game, not the Steam version.

Good to hear that : ) Thank you for your answers.