If you're in the air, you only need to pass those elements of the flight plan which ATC require in order to issue you with a clearance (for Class D). This is true for both IFR and VFR.
You need to file a flight plan to operate IFR (including operating under IFR as a VFR flight) in Class D - but booking out should be sufficient for light aircraft VFR departures (subject to the distance/weight/international rules).