Thank you for the explanations. To make it simple I reinstalled the game via steam I put the custom dlcs in the steamapps/common/dlc folder but they did not appear, it was other dlcs that appeared. After different tests I found an identical folder steamapps/common/dlc on a hard disk on my computer. The game launches the dlc which are there and not that of the programesfiles86. So I don't really know how to make everything go back to normal but in any case it works...