by For adding a script named MyScript.bat to the context menu for all files, create a .REG file to modify registry:
Windows Registry Editor Version 5.00 [HKEY_CLASSES_ROOT\*\shell\MyScript] @="Run MyScript" "Icon"="C:\\path\\to\\your\\icon.ico" [HKEY_CLASSES_ROOT\*\shell\MyScript\command] @="C:\\path\\to\\your\\MyScript.bat \"%1\""
Double-click the .reg and confirm to modify the registry
The %1 is the file to be passed as an argument to the script
For specific file types: HKEY_CLASSES_ROOT\.txt\shell instead of HKEY_CLASSES_ROOT\*\shell\MyScript