A documentary, five years in the making, about the slow-footed race-against-time to finish an epic “three volume” biography of Lyndon Johnson’s fifth and final volume before the researcher/author and his editor pass away from very old age is nobody’s idea of an easy sale — not to a film distributor, nor to most filmgoers.

Even the title — “Turn Every Page: The Adventures of Robert Caro and Robert Gottlieb” — seems ironic, if not oxymoronic. “Turn every page” and “adventures?”

But filmmaker Lizzie Gottlieb (“Romeo Romeo” was hers), daughter of 90something editor Robert Gottlieb, has produced a filmed appreciation not just of her father and the Pulitzer Prize-winning Caro and their epic final collaboration. It’s a film about a decades-long deep dive into “power” in America and a monument to a sort of life-long collaboration we will never see again.

“Turn every page” was a discipline passed on to Caro, he recalls in the film, by his New York Newsday (newspaper) editor Alan Hathaway. As Hathaway promoted Caro to investigative reporter, the trait he noticed in Caro’s research was his thoroughness. “Turn every page” when you’re digging into something, Hathaway preached.

This process, this degree of care and determination to nail down facts and expand a story as much as need be in order to write something unimpeachable and definitive is what “Turn Every Page” celebrates.

When we see a recent Caro visit to the LBJ Presidential Library in Austin, Texas, later in the film, he notes that when he first started researching the life, rise to power, triumphs and failings of Johnson, there were “thirty-two million pages” of documents, letters, telegrams and records there. “Now, it’s forty-five million.”

And if you’re as dogged and exacting as Caro, that’s a reading challenge you have to accept, even as he passes his 87th birthday. Because if you want to answer conclusively whether or not Johnson stole the 1948 Democratic Senate primary in Texas, you have dig just that deep.

Lizzie Gottlieb, who interviews the two men — although, at Caro’s insistence always separately — takes care to present their achievements together and as individuals.

Caro is known for his LBJ books and the massive tome that preceded them, 1974’s “The Power Broker,” about New York toll road authority chief Robert Moses.

An opening montage of many pundits, experts and politicos appearing on Zoom call TV appearances, shows this book on the bookshelves in the background of their home offices, “a credential,” Lizzie Gottlieb narrates, not unlike a diploma hanging on the wall. If you want to understand “power” in America, this thousand-plus page tome is essential reading to this very day.

It’s a book that shows how Moses, “never elected” to any political office, wielded power in New York city and environs, “rebuilt” and re-imagined the city, both for convenience and as an aid to future growth and quality of living. And as Moses, whose toll roads/toll bridges position gave him staggering sums to work with, repaid favors and curried favor with politicians and real estate and construction tycoons, he literally bulldozed communities and those who lived in them.

Caro learned his mission wasn’t just to study power, how it was obtained and exercised, but to understand and impart to readers “the effects of power on the powerless.” And that’s one reason this book endures and sits on so many book shelves of those who observe American politics and policy. It speaks to generations far beyond its publication date because some things never change.

For instance, I’m writing this review of “Turn Every Page” in Florida, which — whatever its other idiosyncrasies, quirks and right wing politics — leads the nation in the number of miles of toll roads, run by the same sort of authority that made Robert Moses all-powerful. Who does that authority actually work for? Caro gave us the answer.

Gottlieb’s Dad is “the Dumbledore of publishing,” who turned his assertion that he is “a better reader than anybody else” into a career that saw him guiding the works of Caro, Toni Morrison, Salman Rushdie and legions of others to press, zeroing in on details, from punctuation and character development to plot.

At one point, we see him touring a bookstore with his grandson, pointing out books that he edited. He picks up Joseph Heller’s “Catch-22” and tells the kid and us of how he talked Heller out of “Catch-18” as a title.

The two contemporaries, Jewish New Yorkers, are giants of their professions, “Turn Every Page” reminds us. How they manage to work together, their debates over what to edit out, what to change and when or when not to use “semicolons” make for a fascinating dive into that process for any reader who sees this film.

We see Caro note how many words he writes or rewrites every day, the old fashioned “carbon copy” he makes of every typed page and his not-wholly-haphazard way of storing these backups. We learn that he and his actress and research back-up wife, Tony-nominated actress Maria Tucci, moved to Texas for three years. That’s how Caro made great progress in researching Lyndon Baines Johnson, learning about the hard Hill Country childhood that shaped the president who passed Medicare, Medicaid, The Voting Rights Act and landmark civil rights legislation as part of his “Great Society” agenda. It’s where Caro got a handle on a giant figure so “insecure” that he stumbled into Vietnam, and the many other traits and missteps that mar Johnson’s “ends justify the means” legacy.

Gottlieb, who has done quite a bit of writing of lighter (shorter) non-fiction and biographies, who ran The New Yorker for a spell, and had time to be heavily involved in the running of The New York City Ballet, comes off as more whimsical, acknowledging and mocking his ego and accommodating his filmmaker-daughter, cracking that “I was a good Dad” as they sit for another interview.

What emerges is an affectionate portrait of these two and their collaboration, perhaps with some of the rougher edges rubbed off, perhaps not as deep a dive as Lizzie Gottlieb herself would have liked. It’s still an amazed appreciation of what they’re attempting to finish, late in life, a fifth Johnson book that will, like the Moses volume, be the last word on a seminal figure in American history, another manipulator of American political power and the things a better-informed-electorate will learn about this country just by reading these books.

Rating: PG

Cast: Robert Caro, Robert Gottlieb, Ina Gottlieb, Maria Tucci, Bill Clinton, Conan O’Brian and Lizzie Gottlieb

Credits: Directed by Lizzie Gottlieb. A Sony Pictures Classics release.

Running time: 1:52