At Age 13, Creating the Pentagon Papers. Photocopies, at Least.

There they were at lunch at an outdoor restaurant in the Brentwood neighborhood of Los Angeles, that afternoon in the fall of 1969, a divorced father and his 13-year-old son. The father said he had some papers that he wanted to copy. Would the son help?

“I said, ‘Yes, sure,” the son recalled. Off they went to a Xerox machine that was big, clunky and, by today’s standards, very, very slow.

It was the first time anyone had let the son run such a monster. He was thrilled.

Saying that the father wanted to copy “some papers” is like saying that the Vatican is “a church.” The papers — which the father was smuggling out of his office, a briefcase-full at a time — would become known as the Pentagon Papers, the sprawling, classified history of the Vietnam War. The father was Daniel Ellsberg, a former Defense Department official who by then was deeply discouraged about the conflict.

The son, Robert Ellsberg, may have had a cameo role in history as his father’s helper, but not in the film “The Post,” Steven Spielberg’s drama about the newspaper that played catch-up after another newspaper — this one — broke the story of the Pentagon Papers.

There was no 13-year-old at the Xerox machine in the movie, only grown-ups, but then, there was a lot of copying to be done, Mr. Ellsberg’s father put him to work only twice and moviegoers expect edge-of-your-seat action. Old-fashioned Xeroxing — slapping a single sheet of paper on a glass plate, pushing a button, waiting for the copy to print out, then doing it all over again with the next page — is anything but.

“It’s funny about the film,” Mr. Ellsberg said. “At one of the premieres, Steven Spielberg said there were things we would have liked to have put in this film that nobody would have believed, like that Ellsberg brought his kids to help copy the papers.”

Mr. Ellsberg knows that because he read it somewhere — no V.I.P. screenings for him. He paid for his own ticket to see “The Post” at a theater in Pleasantville, N.Y. No one in the audience realized that the fingerprints on someone’s bucket of popcorn would have matched fingerprints the F.B.I. found on the Pentagon Papers. As he dryly put it, “I didn’t introduce myself.”

He has been happy not being in the limelight or his father’s shadow — he said that for years, he did not want to be remembered as “Robert Ellsberg, son of Daniel Ellsberg.”

“I wanted to be my own kind of person,” he said, adding that he had never given a long interview until we spoke last week.

But “The Post” has people calling. The Harvard Divinity School posted a question-and-answer session with Mr. Ellsberg on its website. And on Saturday, he will take part in a conversation at the New-York Historical Society that it says is intended “to help young visitors better understand one of the biggest scandals of the 20th century and the role that one kid played in it.”

Read more at The New York Times.