PSIDuck: 1) Move the Files from ALL cd's in a folder. Name it for example Witcher 3
2) Download this: adfly/1Hgzrn (Direkt Download)(i removed the dots, you need to put them manually, because youre not allowed to post links. simply put a "." between "ad" and "fly" and add "http://" before it)
3) Rename your setup.bin files like this: setup_the_witcher_3_wild_hunt_2.0.0.28-1
setup_the_witcher_3_wild_hunt_2.0.0.28-2
setup_the_witcher_3_wild_hunt_2.0.0.28-3
setup_the_witcher_3_wild_hunt_2.0.0.28-continue with this
4) Start the downloaded file and it installs!
5)HF
FYI, step 2 won't work because that link is specific to your account. Use this instead:
Note: You'll need to have the game on your account and be logged in for it to work. If you don't already have the game on your GOG account, there should be a code to redeem it on the back of the game manual :)