Winstonhusky: I bought The witcher 3 from Gog, but, my download speed is sucks only 50KBps, and it may take weeks to finish the download for 27GB.
I have a friend who bought The witcher 3 in steam, So I want to copy his game client to my Gog.
Is it possible guys? thank you
To answer your specific question, no it is not possible to do what you're asking. To try to solve the underlying problem however which is that you want to get the game as soon as possible there are 3 different ways you can download and install your games here on GOG at the moment. If one of them is acting slow for you, you can try one of the other ways and it might be much faster. The 3 ways are:
1) GOG Galaxy - which is probably what most people new to the site and many others are using currently because it is prominently displayed on the front page and elsewhere and people are encouraged to try the beta. The beta is incomplete and some people report having problems with download speeds with it. This could be due to bugs in the software that are not ironed out yet, or due to slow servers or other problems specific to a particular country or region.
2) GOG Downloader - which is the main way people downloaded their games before Galaxy and probably still the main way most customers that have been here for a long time still use. GOG Downloader is fairly stable and has been around forever. It also uses different backend servers from Galaxy so performance problems on one service do not affect the other.
3) Directly downloading the game installer from the website library and installing it manually. I believe this gets its files from the same place that GOG Downloader does so they should in theory have the same performance characteristics. For large game files many people find the GOG Downloader to be more reliable than using a web browser to do their downloading however.
If none of these methods perform well enough, you can contact GOG support and they may be able to provide further assistance. Ultimately they want to give you the best experience they can and if you're not having it then they want to help.
Hope this helps and welcome to GOG.com.