Not having teeth isn't a problem. Why is there a pin in the jaw? Six is pretty young to have lost all the teeth due to dental disease, but if this dog was malnourished for a long time and during tooth development, could be the reason. Many dogs will continue to gum hard food, so you may not even have to have special diets.
Sounds like this poor puppy needs a good home.
Doug, DVM
Doug & Sandy
Kaylee
Winnie 6 1/2 year old golden
2008 Southwind 2009 Honda CRV