I do belive you can switch your puppy to adult food as long as it is a high quality pet food. There are so many out there that claim to be, especially the breed specific...hint hint.
Check out this web sight. It really opened my eyes about dog food misconceptions and false advertising!
Dog Food Comparison, Ratings, Reviews - In-Depth Guide to the Best Dog Food
I have switched all 3 of my dogs to 1 food for the 1st time in 7 years!!! I had been buying 1 for the sensitive stomach one, 1 for the picky eater, 1 for skin allergies. Then trying to keep all 3 from eating each others food...what a circus!! Found the right food for a 3 and all 3 love it!! It has healthy ingredients. I have seen improvement in all 3 dogs!
Hope this helps!