Thanks for the replies and it is good to know that the amulet rings are included in the documentation.
But can someone from GoG confirm if the copy protection is disabled throughout the game (I don't want to decipher the rings to play the game).
The codes were present in the addendum "Amulets" or something like that.
The GOG version offers them in two jpg files as it has been said before.
The game asks for the codes when you enter the sanctuaries to enable them, but apparently you can type anything and it does work. So If that's the copy protection you are referring to, then I can confirm it is disabled.
But I ignore if the game had any other different kind of copy protection present (non mentioning the spell names into the manual, of course).