You can open and edit any text file using any of the available text editors. You do not need to convert anything, just rename the suffix should you need it. However, you may need to save it using proper coding when saving your file. This is often used when you mod scripts for computer games, including Call of Duty (.gsc scripts).
Convert Text file to Call of Duty script file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert text to gsc on Windows
A sophisticated source code editor for programmers
Convert from text file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.