They are already publicly available. You can access up to, IIRC, $30 worth of PACER for free each month. I know my access usually comes under the free boundary.
But as poster below mentions, it depends on how the documents exist. There are two types of documents in a court case: common law record and discovery.
Discovery = evidence kept by both sides, but not held by the court. This includes written documents, audio/video recordings, but also the transcripts of any depositions that have been taken of important people in the law suit. (A deposition is where you sit down with a person and question them under oath outside of the court room)
Common law record = anything that is said in court, or filed in court.
Most discovery never makes it into a court room. It is just shuffled back and forth between the plaintiff and defendant.
Now, when it comes time to file a motion (let's say one of the parties tries to get the case dismissed) then it will usually be necessary to attach some documents as exhibits to the motion to clarify the point you are making to the judge. At that point, those documents will make it into the public record and will be in PACER.
Even if something isn't filed in court, if the court case is USA v. TechBro, for instance, then as the USA is a governmental entity it is subject to FOIA and you can often get a copy of all the discovery that way. I often use FOIA just to avoid PACER fees.