Purina Pro Plan is a premium complete food used by many breeders. You should keep your puppy on the same food his breeder was feeding him for at least a week or 2 & if you do decide to change to another brand, then this should be done slowly & gradually over a period of days to avoid upsetting his tummy. I don't use Pro Plan myself but know quite a few people who do - it has a good reputation in breeder circles.
Jane