What exactly is an SEC filing? Is it like a quarterly earnings report, a press release? I could not understand much from the wikipedia link.
Can you give an example where reading SEC filings has helped your trading/investing (a.k.a you found info that you did not find on wall street journal or a major business channel)
There are many different kinds of SEC filings with different purposes. Broadly speaking, what they have in common is that they are the ways that companies publicly disclose information that they are legally required to disclose. The page that you listed gives brief descriptions of many types, but if you click through to the articles on individual types of filings, you can get more info.
One of the most commonly discussed filings is the 10-K, which is, as Wikipedia says, "a comprehensive summary of a company's financial performance". This includes info like earnings and executive pay.
One example of a form that some people believe has potential utility for investors is Form 4, which is a disclosure of "insider trading". People with a privileged stake in a company (executives, directors, and major shareholders) cannot legally buy or sell shares without disclosing it by filing a Form 4. Some people think that you can make use of this information in the sense that if, for instance, the CEO of Google buys a bunch of Twitter stock, they may have some reason for thinking it will go up, so maybe you should buy it too. Whether such inferences are accurate, and whether you can garner a practical benefit from them (i.e., whether you can manage to buy before everyone else notices and drives the price up) is debatable.
My personal opinion would be that, for an average retail investor, readng SEC filings is unlikely to be useful. The reason is that an average retail investor shouldn't be investing in individual companies at all, but rather in mutual funds or ETFs, which typically provide comparable returns with far less risk. SEC filings are made by individual companies, so it doesn't generally help you to read them unless you're going to take action related to an individual company. It doesn't generally make sense to take action related to an individual company if you don't have the time and energy to read a large number of SEC filings to decide which company to take action on. If you have the time and energy to read a large number of SEC filings, you're probably not an average retail investor. If you are a wheeler dealer who plays in the big leagues, you might benefit from reading SEC filings. However, if you aren't already reading SEC filings, you're probably not a wheeler dealer who plays in the big leagues.
That said, if you're a currently-average investor with big dreams, it could be instructive to read a few filings to explore what you might do with them. You could, for instance, allocate a "play money" fund of a few thousand dollars and try your hand at following insider trades or the like. If you make some money, great; if not, oh well. Realistically, though, there are so many people who make a living reading SEC filings and acting on them every day that you have little chance of finding a "diamond in the rough" unless you also make a living by doing it every day.
It's sort of like asking "Should I read Boating Monthly to improve my sailing skills?" If you're asking because you want to rent a Hobie Cat and go for a pleasure cruise now and then, sure, it can't hurt. If you're asking because you want to enter the America's Cup, you can still read Boating Monthly, but it won't in itself meaningfully increase your chances of winning the America's Cup.
I use 10-K and 10-Qs to understand to read the disclosed risk factors related to a business. Sometimes they are very comical. But when you see that risk factor materializing you can understand how it will effect the company.
For example, one microlending company's risk factor stated that if Elizabeth Warren becomes head of the Consumer Financial Protection Bureau we will have a hard time... so we are expanding in Mexico and taking our politically unfavorable lending practices there.
I like seeing how many authorized shares there are or if there are plans to issue more.
An example was where I heard from former employees of a company how gullible the other employees at that company were and how they all thought they were going to get rich or were being told so by upper management. Poor/Quirky/Questionable/Misleading management is one of my favorite things to look for in a company so I started digging into their SEC filings and saw that they were going to do a reverse split which would make the share prices trade higher (while experiencing no change in market cap), but then digging further I saw that they were only changing the already issued shares, but keeping the authorized shares at the much larger amount of shares, and that they planned to do financing by issuing more of the authorized shares. I exclaimed that this would mean the share prices would drop by 90%-99% after the reverse split and you mean to tell me that nobody realizes this (employees or the broad market). I was almost tempted to stand outside their office and ask employees if I could borrow their shares to short, because there wasn't enough liquidity on the stock market! This was almost the perfect short but it wasn't liquid or have any options so not perfect after all. It traded from $20 after the reverse split to $1.27
I like understanding how much debt a company is in and the structure of that debt, like if a loan shark has large payments coming up soon.
This is generally what I use those particular forms for. But they contain a lot of information
A lot of companies are able to act they way they do because people do not read.
