It is known, that if you put game files into steam directory and install game, steam will see those files so there's no need to download them. I've got Shadow of Mordor(42Gb) already on my HDD, but I don't have another 42Gb of free space, that steam asks for before it proceeds to checking files or downloading. Is there a way to install it like this, to trick steam or bypass free space check?
Do you have an external drive? If yes:
- Copy the Game to your external drive
- Delete the Game from your HDD
- Start the download
- Stop the download, close your steam application (so that there are no read/write conflicts)
- Copy the game files in the correspoding location on your HDD (something like Steamapps/Common/ShadowsOfMordor) from your external drive
- Reopen Steam. It should detect that the files are now there.
Accepted answer is not quite full: beside copying contents of
steamapps/common/<game_name>, you should also copy
steamapps/appmanifest_xxx.acf file of your game. Those
.acf files are plain text, so you can find one for specific game by opening them with notepad. Also, you may want to edit installation path inside this
.acf file, e.g. replace disk "C:" to "D:".
See this community post for more details: https://steamcommunity.com/discussions/forum/1/1729827777350389329/