Help with Drop Down Box - Expand or Collapase

[Loss1003]

The following code is not working as I'm trying to Expand or Collapse with Drop Down Box in Word 2010

Sub Dropdown4()
If FormFields("Dropdown4").DropDown.Value = "Observed" Then
ActiveDocument.Bookmarks("RiskTData").Range.Font.Hidden = False
End If
 
If FormFields("Dropdown4").DropDown.Value = "Not Applicable" Then
ActiveDocument.Bookmarks("RiskTData").Range.Font.Hidden = True
End If 
 
If FormFields("Dropdown4").DropDown.Value = "Not Observed" Then
ActiveDocument.Bookmarks("RiskTData").Range.Font.Hidden = True
End If
End Sub

Please assist with any errors per the above code. Thank you.