Maxred: filing a flight plan certainly does NOT 'take care' of PPR.
If the airfield is unlicenced for instance, you must still get permission on advance to use the aerodrome before you file a flight plan.
I work part time at an unlicenced airfield where the runway is given away for non-aviation use for long periods, but the airport operator will try to fit you in when they can. If you turnup without having been granted permission to land, you will probably find the owner/operator denies permission for you to use his land.