You shouldn't be using editable fields in the header for the simple reason that the user has to open the header in order to access them. Put them in the body of the document and if you want to repeat them in subsequent page headers, either use mapped content controls or in the case of form fields use REF fields.
You should not mix form fields and content controls in the same document. Physically then can be mixed, but it makes any automated reading and recording the form data subsequently far more difficult than it needs to be - see
Extract data from forms
If you are using content controls, the document doesn't need to be protected for forms as that imposes all sorts of restrictions. You could instead use 'editors' applied to the controls and apply read only protection. You may find
Insert Content Control Add-In useful as a means of inserting controls and applying 'editors' and protection.