NEW YORK (AP) — Not everyone believes that Philip Roth has written his last book.

Among the skeptics: Livia Manera Sambuy, co-director of an upcoming PBS "American Masters" documentary about the prize-winning novelist.

"Philip Roth: Unmasked" features extensive interviews Sambuy conducted with Roth, who turns 80 this month, along with commentary from such friends as Mia Farrow and admiring authors such as Jonathan Franzen and Nathan Englander. The film will air March 29 on PBS stations, but also has a weeklong theatrical run — admission is free — starting March 13 at Manhattan's Film Forum.

The documentary outlines his life and work, from his childhood in Newark, N.J., to such controversial novels as the ribald "Portnoy's Complaint" to his current status as literary eminence and perennial Nobel candidate. But "Unmasked" leaves out Roth's news-making decision, which he revealed last fall, to stop writing novels. He is presented as an active writer, with shots of him at work in his Connecticut home.

Roth not only says nothing about wanting to retire, but declares he would be miserable if he did.

"I keep doing it. I never quit," he says. "My worst times are when I'm not writing. I'm prone then to be unhappy, depressed, anxious, and so on."

Through the publication of "Nemesis," which came out in 2010, Roth had been dependably turning out a book a year. But he released no new work in 2011 and by last fall had informed the French magazine Les inRocks that "Nemesis" was the end. A wave of reports followed, and Roth has said he is relieved and delighted to be done.

"Someone should have told me about this earlier," he joked about his retirement during a discussion in January with the Television Critics Association.

In a recent email interview, Sambuy acknowledged that she and friends of Roth knew during filming that he had decided to quit. Although the voluntary silence of a celebrated, apparently healthy writer is rare in literary history, Sumbuy said that "no one imagined" it "would be such big news." And she doesn't think he's really given up.

"I would have considered adding a postscript had I actually believed he could ever stop writing," she explained. "As Mia Farrow says in the film: 'Sometimes he's said that that's his last book. But I've heard that, and I don't believe it anymore.' For what it's worth, I don't either."

Roth declined to comment for this story.

The PBS documentary originates from "Roth On Roth," a 52-minute film Sambuy collaborated on with French filmmaker William Karel in 2010. (Additional interviews for "Unmasked" were conducted in 2012). An Italian journalist who has spoken with the author several times over the years, Sambuy says Roth himself suggested the original project in 2009 while they were dining together in New York — a conversation that began with her seeking recommendations for other writers to interview.

"Not only did he offer the advice I was asking for — this is something I was counting on, as he had been very generous and engaged in at least one past similar occasion — but at the end of our conversation he said, 'When are you asking me?,'" she recalled. "I thought he was playing cat and mouse, but no, he had already made up his mind."

The "unmasking" is partial in other ways. Few details are given about his private life, including his brief marriage to actress Claire Bloom, beyond his dating often while an undergraduate at Bucknell University. The film does portray a close bond with Farrow and how she unintentionally provided material for his work. A concert they attended together ends up in his novel "The Human Stain." Her childhood battle with polio informs "Nemesis," in which Roth imagined an epidemic in New Jersey in the 1940s.

"I saw a lot of what I told him, but translated into something else," she says in the movie.

Roth is characteristically feisty, witty and direct. He disparages the idea that he is a "Jewish" writer — "I don't write Jewish, I write American." He remembers objections from the Jewish community to his breakthrough book, "Goodbye, Columbus," for its references to a girl who buys a diaphragm and a married man who has an affair: "I maintain there were Jewish girls who bought diaphragms, and there were Jewish husbands who were adulterers," he says.

Roth also discusses such literary heroes as James Joyce and Saul Bellow. He remembers the madness of "Portnoy's Complaint," which came out in 1969 and made him a celebrity, with strangers calling out to him and a cab driver named Portnoy complaining that passengers teased him about the novel's sex-obsessed narrator. Roth speaks of his career in the present tense, but he also has a lot to say about mortality. Noting that a book (by Blake Bailey) is being written about him, he jokes that he has "two great calamities to face," death and his biography, with the biography hopefully arriving first.

"What interests me here, in retrospective, is that his not being at work on a book is one of the things that made this film possible," Sambuy said. "Judging from how I know him, had he been writing Roth would have lived through the interviews with the impatience of someone who is being unjustly distracted from his very absorbing and much more important work."