To elaborate on Stefan's response...
The idea of this type of form is that you:

1. Create a Template of your form. You put in the fields and protect it for filling in forms.
2. You use that template to create a new Document that has the form.
3. You move from field to field in the form using the tab key and fill out the fields. The form stays protected.

If this scenario is not what you have in mind, what is it you are trying to do? Word may have different tools better suited to meeting your objectives.