By the summer of 2015, Mr. Cooper went further. He proposed that Mr. Whitaker get personally involved in a dispute with a man who was apparently a disgruntled former employee of Mr. Cooper’s at a different business. The man had threatened to complain about him and World Patent Marketing to the Better Business Bureau.

On the afternoon of Aug. 21, 2015, Mr. Cooper sent a proposed draft of a letter he had ghostwritten for Mr. Whitaker to send to the complainer, invoking his status as a former federal prosecutor and member of the firm’s advisory board and threatening the man with “serious civil and criminal consequences” for what he suggested was tantamount to blackmail or extortion.

Mr. Whitaker made a few minor changes to the draft and hit send. In all, he had spent about six minutes from receiving the proposed draft to inserting himself directly in the dispute, as Mr. Cooper had hoped he would do.

That email from Mr. Whitaker later became part of the litigation over World Patent Marketing, and was cited as a message he sent to one of the firm’s customers in news articles in recent weeks about how his activities with the now-defunct firm were dogging his appointment to be acting attorney general.

Federal Trade Commission investigators were immersed in such exchanges last fall when they subpoenaed Mr. Whitaker’s former law firm on Oct. 5, 2017, and tried to get in touch with him about why he was not responding to it — just as he was being hired as chief of staff to Mr. Sessions. But the agency was initially unaware of his turn of fortune.

Among the files released on Friday were an email and a voice mail message to Mr. Whitaker from Mr. Evans, in which he noted it was his second attempt to reach Mr. Whitaker. Mr. Evans said he needed four or five minutes of Mr. Whitaker’s time by phone to discuss his relationship with World Patent Marketing.

A second voice mail made public was Mr. Whitaker’s response to Mr. Evans. He said he had not been aware of the subpoena previously, and then he shared his news: “I am now at the Department of the Justice here in Washington, D.C., as the chief of staff to the attorney general. So I want to be very helpful.”