Use Action wizard to insert document level javascript for 'Will Close' event

Hello! I have used JS and Action Wizard to insert document level script to turn off the form field highlights:

this.addScript("Turn Off", 'var highlightPref = app.runtimeHighlight ;
app.runtimeHighlight = false ;');

And I have the code that will reset the user's preference:

app.runtimeHighlight = highlightPref ;

I know that I can paste this into the Document Actions and it works perfectly. BUT I have many hundreds of pdfs that require this code, and I am trying unsuccessfully to find/write the code to insert the Document Will Close action using Action Wizard so I can batch process them. Can anyone help please?