it's not enough to leave the file there. You have to leave bittorrent running. Once your client finishes downloading, it will remain open until you click the Finish button. This is known as seeding. You can also start a BT client with a complete file, and once BT has checked the file it will connect and seed the file to others. It is good to continue seeding a file after you have finished downloading, to help others finish.
Right now i'm showing zero seeds, which means noone who has the full file is still sharing it.