I created a fillable Word 2013 document and protected it through Restrict Editing.

I selected 'Editing restrictions', and selected 'Filling in forms' from the drop down box.

I then selected 'Start enforcement', entered a password, and I was done.

Although it restricts editing text, it allows additional lines to be created by hitting the Enter key.

How do I protect ALL editing except for access to the fillable fields?