This database opened on the Internet in 1994 (it was one of the first major government-sponsored datasets offered this way). It covers public filings by U.S. public companies made to the SEC from that data, this includes such things as 10K, 10Q, annual, quarterly reports, and many other items.

This database only covers filings made from 1994 on, for public consumption, and when made electronically by the filing company. Thus, it does not cover earlier years, current paper fillings, or non-public ones.