Have a look at the following article:

http://word.mvps.org/FAQs/MacrosVBA/CreateAMacro.htm

What you then need to do is have some way of running the macro from the
form. There are various ways to do this, and you may be better off looking
at a more general Word programming forum, but for example you can go into
Word Tools|Customize|Commands, select category macros, selectyour .doc in
the drop-down at the bottom, then find the macro in the list of macros and
drag it to a toolbar.

Then protect your Form document, fill in the fields, and click the button
you just created. To work the document needs to be connected to a data
source. off the top of my head, I can't remember whether you can set that
up, then protect a form without losing the connection. If not, you'll need
to do a couple of additional things. But have a go at that for now.

Peter Jamieson