What version of Word? Have you considered using content controls instead of Formfields?
Private Sub Document_ContentControlOnExit(ByVal ContentControl As ContentControl, Cancel As Boolean)
Dim oCC As ContentControl
Dim oRng As Word.Range
Dim strPW As String
strPW = "topics"
Select Case ContentControl.Title
Case "Subject" 'The "Subject" Dropdown CC in document.
If Not ActiveDocument.ProtectionType = wdNoProtection Then
ActiveDocument.Unprotect Password:=strPW
End If
Set oCC = ActiveDocument.SelectContentControlsByTitle("HF Subject").Item(1) 'Richtext CC in Header
Select Case True
Case ContentControl.ShowingPlaceholderText:
oCC.Range.Text = vbNullString
Case ContentControl.Range.Text = "MATH"
oCC.Range.Text = "Subject: MATH"
Set oRng = oCC.Range
oRng.Start = oRng.Start + 9
oRng.Font.ColorIndex = wdRed
Case ContentControl.Range.Text = "ENGLISH"
oCC.Range.Text = "Subject: ENGLISH"
Set oRng = oCC.Range
oRng.Start = oRng.Start + 9
oRng.Font.ColorIndex = wdBlue
Case ContentControl.Range.Text = "SOCIAL STUDIES"
oCC.Range.Text = "Subject: SOCIAL STUDIES"
Set oRng = oCC.Range
oRng.Start = oRng.Start + 9
oRng.Font.ColorIndex = wdGreen
End Select
'Richtext CC in Footer
ActiveDocument.SelectContentControlsByTitle("HF Subject").Item(2).Range.FormattedText = oCC.Range.FormattedText
ActiveDocument.Protect wdAllowOnlyReading, , strPW
End Select
lbl_Exit:
Exit Sub
End Sub