The free software "ClipboardPath" adds a new command "Copy Path to Clipboard" to the context menu for files and folders. Pasting the complete filename or foldername into any dialog or editor is just a mouse click away. You always get the full path.
(Freeware, 120 KB, Version 1.2)
Just click with the right mouse button on any file or folder and select "Copy Path to Clipboard". Now the full pathname is in clipboard and can easily be pasted into e.g. text editors, email editors or file dialogs. If you hold down Ctrl while clicking, a local network path will be converted to the corresponding UNC path (\\server\share\...)