Jen,

If you use a protected form you can run a variation of the
following macro run on exit from the mandatory field:

Sub ExitText1()
   With ActiveDocument.FormFields("Text1")
       If Len(.Result) = 0 Then
           Beep
           Application.OnTime When:=Now + TimeValue
("00:00:01"), Name:="GoBacktoText1"
               Set Balloon = Assistant.NewBalloon
               With Balloon
               .Text = "No Data!" & vbCr & "You must fill
in this FormField"
               .Button = msoButtonSetOK
               .Animation = msoAnimationBeginSpeaking
               .Show
               End With
       End If
   End With
End Sub

Sub GoBacktoText1()
   ActiveDocument.Bookmarks("Text1").Range.Fields
(1).Result.Select
End Sub

By variation, I mean you will have to make a macro and
change "Text1" to the bookmark name of each mandatory
field.