Use of reference fields in Order, Shipment and Billing

Hi,

I configure odt templates for proposal, order, shipment and billing. I find in the standard delivered PDF templates on the printout referenced information. E.g. on the shipment I found the number of the order as well as the order date.
I also like to use such information on an odt based template but wondering about how to do it. May I oversee it in the documentation and so every hint how to do it or information that it is not possible will be appreciated.

Regards,
Christian