I recently built a PC from spare parts and am trying to move my complete and patched Skyrim folder over to the new rig. I used the instructions in the pinned topic to install the basic game from disc, but it only amounts to 44% of the total. Steam wants to download the rest (addons/DLCs). I backed up the game from the my main PC and copied it over to the Steam/SteamApps/Common/folder, but Steam insists the game is not ready to play and wants to download the other 56% (even though the complete game is now in the Steam folder). Is there any way to migrate Skyrim over to a new PC without hours of download? I have a fairly slow internet connection and 56% translates to about five hours. Thanks.

Choose install from backup in the Steam menus.

You have to use Steambackup.exe to use your archives to install a game.

https://support.steampowered.com/kb_article.php?ref=8794-yphv-2033

Thank you - had no idea there was such a thing!