required field needs to be filled out before moving on to next field

You think you want that but you actually don't. Consider reversing the process. Make any fields that are actually dependent on the required field to be read-only (non-editable) until the required field is filled out. For required fields that are just required but have no dependent fields, do a check on them during the doc.WillSave event and remind the user that these fields are required but don't force the filling; they might be saving until they get the right information. If there is a submit button on the document, by default, submit won't work until the fields are filled out so you're already covered there.

Required fields only apply when the user clicks submit... and you should consider that people often fill in forms in the order that their mind takes them and the order that information is found; it's a very negative user experience to try and force them to think the same as you...