Robert Moses, whose brilliant and brutal vision yielded a New York City of concrete, and President Johnson, who insisted on both guns and butter, were hard men, obsessed with power and fluent in its exercise. In the years after their respective reigns two Roberts — Gottlieb and Caro, word-besotted Manhattan Jews — coalesced to tell of the city and country Moses and Johnson roughly shaped. 

It was only a matter of time before the biographer and his editor got a biography of their own. “Turn Every Page — The Adventures of Robert Caro and Robert Gottlieb” is a documentary that tells the story of the partnership that yielded “The Power Broker” and the first four books of “The Years of Lyndon Johnson,” with a volume yet to come. Mr. Caro is 87, Mr. Gottlieb 91, giving a film that is about slow writing and careful reading a dash of mortal tension.

“Turn” is directed by Elizabeth “Lizzie” Gottlieb, who sought to capture the half century of collaboration between her father — who headed Simon and Schsuter, Knopf, and the New Yorker — and Mr. Caro, a Princetonian who got his start at Newsday before jumping to the marathons of writing big books from the sprint of daily journalism. The film begins with the clack of his typewriter keys and the swoosh of graphite on paper. The writing life.

Mr. Caro, who we see wear a shirt and tie to his spartan writing desk and punctiliously ensure that there is a carbon copy for every page he writes, has achieved an improbable celebrity in the TikTok era. We see the talk show host Conan O’Brien promise to be first in line for Mr. Caro’s next book, and the actor Ethan Hawke perform readings of the biographer’s prose. During the pandemic, seemingly every zooming talking head had a copy of “The Power Broker” displayed on a shelf. 

Awards have flowed Mr. Caro’s way, from Pulitzers to National Book Awards to a raft of history prizes to the National Humanities Medal placed around his neck by President Obama. They all seem incidental to what drives him, which “Turn” pinpoints as grappling with how the meetings of men and moments shapes American democracy. Mr. Caro believes that in seeing how power works, we are reminded of our role in its distribution. 

Mr. Gottlieb is hardly a retiring editor, meekly scrawling corrections. “I’m fast,” he brags, and notes that humility has never been in his quiver of virtues. One colleague in “Turn” labels him the “Dumbledore” of publishing, a wizard who has shaped masterpieces by  John Cheever, Toni Morrison,  John le Carré, Salman Rushdie, and others. President Clinton drawls that he would be a “lost boy” without Mr. Gottlieb’s edits.

One way to see “Turn” is as a haute culture  version of “Breslin and Hamill: Deadline Artists,” from four years ago. The earlier documentary looked at the two Irish-American scribes who wrote for everyman, paper folded over a knee on the subway, cup of coffee balanced in hand. Messrs. Gottlieb and Caro, the latter of whom calls himself a “nice Jewish boy,” blend that sense of sechel with the love of sophistication that only born outsiders become insiders can muster. 

“Turn” is full of treats for bibliophiles. Mr. Gottlieb reflects that an editor has to be “cruel to be kind,” and the leader of the New Yorker, David Remnick, marvels at Mr. Caro’s sitzfleisch, or “sitting flesh,” a Yiddish term naming a Talmudist’s  stubborn focus. Mr. Gottlieb recalls that he and Morrison “read the same way,” and Mr. Caro admits to turning to Homer’s hexameter for the opening pages of “The Power Broker.” He was searching for the right rhythm. 

At one point, Mr. Gottlieb laments that Mr. Caro overuses the word “looms,” and editors everywhere will likely identify with that exasperation at their writers’ incorrigible tics. He proclaims that “a semicolon is worth fighting a war over,” and Mr. Caro opines that for nonfiction writing to endure, it must meet the standards of  well-crafted fiction. Mr. Gottlieb reads Cynthia Ozick in bed, beneath his collection of plastic handbags. Art and life get blurred. 

The final scene features Messrs. Caro and Gottlieb wandering the halls of Knopf’s offices, looking for a yellow pencil with which to huddle and edit. They try office after office. They may as well be looking for a dodo’s feather. An employee proffers a mechanical one, which will not do. An unused one is procured, which Mr. Caro insists on sharpening himself. These men of excellence and typewriters and pencils will pass. Who then will write and edit?