Links with an asterisk * connect to tutorials about how to read the documents.
Tax-exempt corporations file annual financial statements, called 990s,* with the IRS that must be made publicly available at their office. They also are available through a public records request to the IRS and through various online sources. The documents include revenues, expenses and highest paid employees.
Foundation Center 990Finder
Many nonprofits also file more detailed financial statements with the relevant state attorney general or secretary of state.
“Federal audits. Nonprofits, state/local governments, and other noncommercial entities expending $750,000+ of federal funds in a year are required to undergo a standardized audit of their financials and compliance. The US Federal Audit Clearinghouse maintains a public database of those audits; it offers bulk downloads of the report data (about the auditee, auditor, findings, and more), as well a tool to search and access individual reports.” — Data Is Plural
SEC for publicly traded companies
10-K annual report* with audited financial statements
10-Q quarterly filing* with financial statements and notes about pending lawsuits, investigations and other risks
8-K* current information of likely significance to shareholders
Def-14 annual proxy statement with executive pay and perks
Public and private companies
Business charters are filed with the relevant state secretary of state and often available online
UCCs are filed with the secretary of state when collateral is put up for a loan