Since their publication in 1971 the Pentagon Papers have been examined seemingly from every possible historical, political, legal and ethical angle.

But to Lisa Gitelman, a professor of English and media studies at New York University, there’s at least one aspect of Daniel Ellsberg’s leaking of top-secret Defense Department documents that scholars have failed to consider adequately: the Xerox technology that allowed him to copy them in the first place.

Actually, make that “copy and recopy.” In a chapter of her book in progress about the history of documents Ms. Gitelman describes the way Mr. Ellsberg obsessively made copies of his copies, even enlisting the help of his children in what she describes as an act of radical self-publishing....