Submit button to a pdf form, no actions tab visible

I'm tying to add a submit button to a pdf form. All the tutorials say that when you add the button there should be an actions tab in the properties panel. But there isn't one when I add the button on this particular document that has a lot of form fields.

When I add a button to a different pdf with no form elements already on it, the actions tab is there. If I copy this button to the pdf with the form elements, the actions tab disappears.

Why is this and how can I change it?

Thanks