Starting with Windows 95, Windows supports file and folder names up to 255 characters in length. See Win Short file names. File extensions are attached to the file name with a dot, and dots can be placed within the file name. For example, letters to friends.pat.sue.sam.doc is a valid name, and the .doc is treated as the extension, because it comes at the end. Following are the valid characters in a Windows file/folder name. See extension.