How do a add an 'office use only' section?

Thank you for contacting us.

We can do this with a hidden Form Collapse and some hidden fields. Here is a quick video:

http://screencast.com/t/tl2PGatxM

Then, these hidden fields can be filled from a form Submissions page when you edit the entries (submissions).

If you need the 'office use only' section to behave in some other way, please let us know.