HOW TO FORCE FILE DOWNLOD TO PC

Well there could be a whole host of reasons. The main one is usually the file path. Try echoing out your filepath and filename and see if it is what you were expecting. I believe file_get_contents requires the full server path or a URL, not a relative path.

PS you may also want to add a check into your method that file_get_contents actually worked, and if not produce an error message.