I doubt the letter just contains isolated personal information such as an address or social security number. Typically, these are simply redacted before filing. The letter might not even be related to the merits of the case. It could, for example, contain a threat of some sort. I have no reason to believe it is. I'm just pointing out how speculative this can get.
Jim's Rules of Carry: 1. Any gun is better than no gun. 2. A gun that is reliable is better than a gun that is not. 3. A hole in the right place is better than a hole in the wrong place. 4. A bigger hole is a better hole.