The .UNKOWN extension is reserved for files that does not have a file association registered with the native operating system. The UNKNOWN extension may simply act as a placeholder until the file's correct association becomes known by the system. .UNKNOWN files can commonly be viewed by being opened in a text editor, such as Windows Notepad, to see its contents. However, the file may not be stored in plain text, in which case it cannot be viewed in a text editor, and may potentially become corrupt by doing so. An .UNKNOWN file can simply be renamed to another extension, once the correct extension is known.