The good new is that ANY drawing can be saved using the SAVE AS option, as a .dwt (template file).
You may want to go into Modelspace and delete any job specific objects.
Don't PURGE it, or do so carefully, because there will be lots of settings and styles which your friend favors
in place in the drawing. The next time you do something for him, use it, and it will already be tweaked just as desired.
It is a good idea to create a library of .dwt files, for different tasks, vendors, etc.. No point in reinventing
the wheel every time you saddle up.
Later just hit the open icon and in the Files of type drop down list choose .dwt to find and access it.