This sort of thing would be a walk in the sun if the dimwits at Microsoft would fix the Word Object modules so that it where accessible while in the Content Control content store events. In the meantime you can use the registry:
You will need to map your "dropdown" content control to an XML part. Put the following code in the ThisDocument module. Run the setup to store the passwords.
Private Sub Document_ContentControlBeforeStoreUpdate(ByVal ContentControl As ContentControl, Content As String)
Select Case Content
Case "Bob"
If Not GetSetting("Demo", "Passwords", "BobPW") = InputBox("What is your password") Then
Content = vbNullString
End If
Case "Jim"
If Not GetSetting("Demo", "Passwords", "JimPW") = InputBox("What is your password") Then
Content = vbNullString
End If
Case "Joe"
If Not GetSetting("Demo", "Passwords", "JoePW") = InputBox("What is your password") Then
Content = vbNullString
End If
End Select
lbl_Exit:
Exit Sub
End Sub
Sub Setup()
SaveSetting "Demo", "Passwords", "BobPW", "12345"
SaveSetting "Demo", "Passwords", "JimPW", "54321"
SaveSetting "Demo", "Passwords", "JoePW", "12321"
lbl_Exit:
Exit Sub
End Sub