When Cuban-Spanish actor Ana de Armas was asked to play Marilyn Monroe in Andrew Dominik’s Netflix feature “Blonde,” she spent months preparing and studying for the role. “It was very important to discover the real woman and bring all of those elements together,” she said Saturday at the San Sebastian Film Festival.

“My idea of Marilyn in the past was quite elementary,” she said at a press conference. “I knew her films and little more. To get to know her story was fascinating for me. She represented the dream that we all want to be. So what could go so wrong? I now respect her much more, and understand her better and could humanize her much more, and give her more credit for the effort she put into things.”

Produced by Plan B and distributed by Netflix, the film is based on the bestselling novel by Joyce Carol Oates,...