From my earliest days of law practice, I have recognized that the files of lawyers contain quite valuable materials that could constitute primary sources for historical research and analysis.
A knee-jerk reaction to that insight is: the attorney-client privilege and its accompanying duty of confidentiality.
I do not regard the A-C privilege as an insuperable obstacle for the reasons adduced in the report of the Ad Hoc Committee on Access to Lawyers’ Files of the Organization of American Historians (comprising four superb legal historians, Kermit L. Hall (chair), Paul Finkelman, N. E. H. Hull, and Stanley N. Katz) titled Historians and Access to the Files of Lawyers dated March 7, 1994.
The only place on the web the report can be found is in a nook of the website of the American Society for Legal History, here:
https://aslh.net/resources-for-doing-legal-history-legacy/historians-and-access-to-the-files-of-lawyers/