See:
Attached is a sample document that is the source the screenshot. Note, the REF field does not update automatically. It may update with a print preview or print. Otherwise, if you use
Ctrl+A and then
F9, it will update the fields.
The checkbox was mapped using the Add-In
Content Control Tools by Greg Maxey, MVP. Graham Mayor provides a somewhat simpler one here:
Insert Content Control Add-In by Graham Mayor, MVP. Either would be much easier for me than doing the mapping by hand.
This can also be done using macros, but you have no control over whether or not the user will permit macros to run.
[Edit: I've added a link to this thread from my page on Repeating Data Using Document Properties Content Controls and Other Mapped Content Controls as an example of a content control that cannot found in the documen property content controls.]