How many flights can be made under EASA permit to fly?
Assuming you mean a temporary Permit to Fly (rather than a 'permanent' one) for an aircraft normally flying under a C of A, then this site states that:


  You will be required
  
  
  to supply a validity period while completing the application.
  Temporary permits are usually issued for less than a month, but you should allow enough time for the flight to be conducted, taking into account weather conditions etc.
  


I'd guess it is intended for an aircraft to be ferried in order to renew its C of A or at the end of its operational life?