You can programmatically trigger actions synchronized with user input in document form fields. You only need to subscribe to the corresponding UI event using instance#addEventListener, and the callback you provide will be called whenever the event takes place:

instance.addEventListener("annotations.focus", function (annotationFocusEvent) {
	// Will log the properties of the widget annotation that was just focused.

Other events that can be used to detect user input in form fields besides "annotations.focus" are "annotations.blur" and "".

For a complete list of events available for subscription, you can check out the API documentation entry for instance#addEventListener.