Using Actions in Switch with the Quick Check, how to?

I have a Switch flow where we want to find how many pages there is in a PDF. I tried to use the Actions in the flow and it can use a Quick Check. To do so it asks for a .cfg file. It has a sample.cfg but where is it.

How should the .cfg look for just do a app.doc.numPages?

Is this enough?
let numbOfPages = app.doc.numPages;

app.vars.numberOfPages = numbOfPages;

Would be nice with some documentation covering this.

Thanks