I didn't read this topic before I purchased the game on Steam. What will happen if I redeem my steam key? Will it be added as second copy which I can gift to my friend?
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If you want to use the Steam key to gift the game to a friend, probably the best thing would be to send them the Steam key and let them redeem the game on their own account.
My understanding is that if you attempt to redeem a Steam key for a game you already own, Steam will reject the key and say that you already own the game (this is a question that gets asked and answered in the Steam forums and other gaming discussion forums from time to time).