There are a whole host of types of filings. Some of them are only relevant to companies that are publicly traded, and other types are general to just registered corps in general.
There are a few really popular ones:
- Form D: investments
- Form 10-K: annual report, often includes earnings
- Form 10-Q: quarterly report, often includes earnings info
- Form S-1: initial registration for IPO
- Form S-4: mergers & acquisitions
- Form S-8: employee stock incentives
... and many more: http://reportstream.io/explore/has-form
How much you can read them depends on the formats:
- Some forms are actually just scanned PDFs, and you have to go read the scans.
- some other form submissions are in a parsed text format
- some others like 10-K's have big fancy HTML versions that are very human readible
- some are an XML-like format
Some companies don't submit their forms on time or at all
- As you may have seen with the recent SUNE (now SUNEQ) earnings debacle... some companies withhold their earnings, and thus the reliability of the information can be wishy-washy if the company isn'y following the SEC filings rules properly.
- In my experience, Private companies tend to not disclose a lot of financial information, so you have to get creative sometimes to deduce things about the financial health of the company.
Overall, reading SEC filings is hard, and for some, the explanations of those filings is worth paying for.
Source: I am currently trying to build a product that solves this problem.