March is my favorite month of the year. It includes the birthdays of both my oldest son and my Dad, March Madness, St. Patrick's Day, and, of course, 10-K season.

Confused? Don't be. A 10-K is simply the official name given by the Securities and Exchange Commission (SEC) to required annual filings. It's a giant business update that's sometimes called an annual report. What's great about these filings is that they're chock-full of information you, as an investor, can use. Typically, they include three years of financial statements, a complete rundown of risks the company faces, and management's review of the business.

Sure, you might be able to find income statement and balance sheet figures from a financial website, but how will you know whether the company's pensions are underfunded? Or how will you determine whether the company has dangerously high stock options expenses? For these types of questions, you'll need to look at the accompanying footnotes to the financial statements themselves. And for that, the 10-K is essential. Fool writer Bill Mann had a close look at the footnotes when he exposed a number of worrying trends relating to GM's pensions.

Sometimes, this data can help explain what's been happening with a stock. Take General Dynamics (NYSE:GD), for example. Its 10-K was filed Friday. On page 57 is a breakdown of its inventory situation, and it looks really good: Raw materials and works in progress are up from the year prior, but finished goods, on aggregate, were down. That's sometimes referred to as positive inventory divergence, and it indicates a firm that's bulking up to meet new demand, which, in turn, indicates higher expected sales. Investors have warmed to the news.

Of course, there's also plenty of legally required mumbo-jumbo in every 10-K, but even that stuff can be, dare I say it, darn entertaining. Take the Yum! Brands (NYSE:YUM) report. On page 17 of its 10-K are all the clues you need to find out where its famous Chihuahua spokesdog went. (Yo quiero Taco Bell.)

Turns out the commercials were the subject of a lawsuit that dates back to 1998. And while an initial settlement was reached on Jan. 15 of last year, now the company is seeking damages from its former ad agency to cover the cost of the settlement. (Hopefully, its latest foray into TiVo-proof ads proves to be less controversial.)

How can you find out whether a stock you own has filed its 10-K? That's easy. First, point your browser to the SEC's website: Then select "Search for Company Filings" to enter the EDGAR database. Next you'll find a screen where you can either enter the name or ticker symbol of the company you're interested in. And that should lead you to a list of filings. Filter the list by typing "10-K" into the field for "Form Type" and -- voila! -- every 10-K the company has filed over the past several years will appear on your screen.

You can also choose to simply search the "Latest Filings" by using the same filter. That'll show you which firms have filed their 10-Ks most recently. Here's a short list of notables I found in performing a similar search:

  • Devon Energy (NYSE:DVN) filed its report last Friday.
  • So did Mellon Financial (NYSE:MEL).
  • Washington Post (NYSE:WPO) put its filing to bed Tuesday morning.

So remember: For investors, this is the most wonderful time of the year. 10-Ks are abundant, which means that information -- key data that can help you build a richer portfolio -- is flowing. And an expert guide, EDGAR, is on hand to help you take advantage. Why not take him up on the offer? Happy hunting, Fool.

Fool contributor Tim Beyers thinks the SEC is the best government agency ever. Tim didn't own shares in any of the companies mentioned in this story at the time of publication. You can find out what's in his portfolio by checking Tim's Fool profile . The Motley Fool has an ironclad disclosure policy .