The Securities and Exchange Commission (SEC) regulates the U.S.'s securities markets ensuring investors make informed investment decisions. Depending on certain asset size, public companies listed in the United States (including foreign firms) are required to file registration statements, periodic reports, and other forms electronically.
Some recent and historical annual reports and financial information are often available on company websites. They are normally located in a section called "company information," investors, "investor relations," or "financial information." On company websites, you can also try a keyword search for "annual report." You can also perform a Google search of the company name investor for example, "Apple investor" or "Apple investor relations" to get to the investor section on the company's website.