Can an individual file a judgment against you and have it reported on your credit report?

Yes. You can file suit as a plantiff or be the defendant in a suit which results in a judgment against you.

This information, like all public records, is picked up by third party vendors who then report them to the credit bureaus.

A consumer can send information regarding themselves, such as dispositions or proof of payment, to the credit bureaus. I do not know what response you would get if you sent legal information on someone other than yourself.