DOS script to Add the `dntz` File Extension to Any Files Without a File Extension

rename.bat

REM Will add the `dntz` file extension to files w/o a file extension
REM in the current directory
for %f IN ("*.") DO ren %f %f.dntz

REM Will add the `dntz` file extension to files w/o a file extension 
REM in the current and any sub-directories
for /R %f IN ("*.") DO move %f %f.dntz

The first parameter for rename can be a relative or absolute file path. The second parameter has to be a filename and only the filename. If you need to recurse through a directory tree renaming as you go, use move instead of rename.