Did you see the PDF of a real letter from the doctor, from the NYT? I can’t copy, you can read it here. Letterhead says:
Lisa Bardack, MD
Chair of Internal Medicine
Diplomate of the American Board of Internal Medicine
(address)
http://www.nytimes.com/interactive/2015/07/31/us/politics/hillary-clinton-doctor-letter.html?_r=0
But she is not "Chairman of the Department of Medicine, Mount Kisco Medical Group" because there is no such thing. "Chair of Internal Medicine" with the MKMG letterhead is legit, and a completely different thing.
The supposed medical records are a hoax.