Documents are not attached to proceedings, they are attached to the record, or included in the record. A process is nothing physical that something else can be attached to. But a process has records.

In your case, it doesn't even seem like proceedings in the sense of a lawsuit, but a redundant way to say attachments to the contract. Probably one party needed to prove that person A or representatives of company A are entitled to execute an agreement. And such proof is attached to the agreement itself or to some other records available for inquiry.