Hillary Rodham Clinton’s campaign released a letter from her doctor on Friday attesting to her health and fitness for office, on a day marked by a deluge of other disclosures about her finances and a new batch of emails from her time as secretary of state. The document releases, coming on a summer Friday, began with a letter from Dr. Lisa Bardack, a physician in Mount Kisco, N.Y., near Mrs. Clinton’s Chappaqua home who said she had treated Mrs. Clinton since 2001. Mrs. Clinton is the first presidential candidate in this election cycle to make public a medical letter about...