The idea behind the Freedom of Information Act is simple: file a request for a document with the government, and they’ll turn it over.
There are, of course, exceptions. The original Act, signed into law on July 4, 1966, listed eight broad exempted categories, including trade secrets, personal medical records, and classified information.
A ninth item ensured it wouldn’t stop there. Section b(3) of the Act says that information can be exempted from disclosure by other statutes. There’s nothing to require that these other exempting statues mention their intent to foil FOIA, and Congress is welcome to write as many of them as they like.