API to access annual reports of public US companies.
SEC EDGAR Data API is a free Finance API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Details from sec.gov.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
The SEC EDGAR Data API is provided by SEC.gov (sec.gov).
Yes. The SEC EDGAR Data API is listed in the Finance category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The SEC EDGAR Data API requires no authentication, so you can start making requests without signing up.
Yes. The SEC EDGAR Data API supports CORS, so front-end JavaScript can call it directly.
Yes. The SEC EDGAR Data API is served over HTTPS, so it's safe to use in production.