Two possibilities, both bad.
The notice is for you, and is a "CC".
You are not the primary addressee, but you have some legal or financial involvement in the matter.
For instance Joe and Ken get divorced. Their property has an ADU (guest house), and you have been a tenant there for 5 years. The court is going to allocate that property in the divorce, and that certainly could affect your at-will tenancy. So you need to know about it because it affects you.
When you have an interest like this, it certainly is fair for you to read the documents. If the matter really has nothing to do with you, then you are to hold the material confidential - posting it on the Internet or giving it to a tabloid newspaper would be the thing not to do.
"CC" stands for Carbon Copy, traditionally, a typewriter would be used with "carbon paper" to make additional copies of the letter; the original goes to the intended recipient and the CC's to others with interest in the matter. You could only get 2-3 carbon copies (tops) out of a letter; for more the secretary would have to re-type the letter. However, with email, there's no limit.
They meant to send you something else. It's important.
Law offices have legal secretaries and mail rooms that produce paper at a feverish pace. They may have put the wrong thing in the wrong envelope. Somebody else got a notice intended for you.
In that case we don't care about their proceeding, but we darn well care about your proceeding! Getting the wrong thing means you didn't get the right thing.
So if you don't recognize anything about the matter you were sent, you need to follow up with the sender PDQ so they can send you the correct material. Hurry up; the clock is ticking. You might be able to get a relevant date rescheduled because of the botched notification, but that's a pretty big "ask" so don't count on it.
Ignoring this won't stop the legal matter.
Generally when your involvement in a legal action is critical, they will serve you - a process server will physically find you and serve you papers. This is less than that, which means you are a lesser player, and the matter is going to proceed on time with or without your involvement.
They think you got certified mail notice because you signed for it. So you will have no standing to protest if the action didn't go your way.
"They sent me the wrong document" will fall on deaf ears, as you had time contemporarily (right now) to followup and get the right document.