the extension of a batch file is ".bat"

Nope, the format of a file is a vital part of a successful batch file. Even if a file with an unknown file format contains working batch file code in it, a batch file will still not be able to read it because of its foreign file extension. If you want the batch file to be able to read the foreign file, then you can set it to rename the mutated file to .bat format and then read it for it to work.

Example:

@Echo off

REN File.Foreign File.bat

CALL File.bat

exit

A batch file is the text file that contains a series of commands that MS-DOS carries out. A batch file is created by COPY CON command after specifying a file name by using extension as .BAT in DOS mode.

You can just open the batch file with notepad and look at the code

You can't download a program that makes a batch file to do what you want to do. You will need to legally learn about hacking, and then write the file yourself.