You are correct that the property tax exemption form does not establish your homestead exemption as to creditors. However, there is no formal declaration to file to establish your homestead as to creditors. As long as own the property and are living there (or intend to return) the property will be exempt. I wouldn't use the form you found at Office Depot.
You don't need to "file" a homestead declaration for creditor purposes unless you are already in a bankruptcy or post-judgment collection proceeding where there is some requirement to designate exempt property.