Flatten PDF using script

We apply stamps to PDF's frequently for approval and would then like to flatten them so the stamp remains and can't be easily deleted.

I can do this by using the flatten script, however i wondered if there is any way to set this up for each PDF that is opened subsequently. At present the script only flattens the current PDF on saving and then when it is closed the script is not available for the next PDF is opened without having to type the script in again.

Is there a way to create tool that retains the script that does the Save As "flatten" process, so that I don't have to type it in each and every time for a newly opened?