Congressional documents originate from congressional committees and cover a wide variety of topics and may include reports of executive departments and independent organizations, reports of special investigations made for Congress, and annual reports of non-governmental organizations. Congressional documents, along with Congressional reports, are part of the U.S. Congressional Serial Set, commonly referred to as the Serial Set.
For more information on the various types of congressional documents, visit this site.
There are a number of online resources where you can retrieve congressional documents. Some are available to the public, and some the University of Chicago subscribes to. Begin with the following: