For versions after 2007 you would want to not use the "filling in forms" restriction, but rather the restrict editing - no changes - with exceptions restriction and possibly use content controls for the areas where you want text. Word 2007, though, does not allow the checkbox content controls.

If for some other reason you want to use the newer content controls rather than legacy forms, checkbox content controls can be added with a macro. If you are OK with the legacy form controls, you might as well continue using them.