On Sunday evening, as well-heeled guests trickled out of a screening of “Becoming Katharine Graham,” a documentary on the fabled former Washington Post publisher, they couldn’t help but remark on how much has changed at the paper, and in Washington.

Under Ms. Graham, from 1963 to 1991, the publication transformed itself from a regional newspaper into one of the country’s leading journalistic institutions. The film traces her life, focusing on the period she is best known for: standing up to the Nixon administration and publishing the Pentagon Papers, which helped change public opinion about the Vietnam War, and Bob Woodward and Carl Bernstein’s Watergate reporting, which led to President Richard M. Nixon’s resignation in 1974.

The premiere was held in a theater at the John F. Kennedy Center for the Performing Arts. Ms. Graham was fond of the arts complex, which President Trump recently took over after saying some of its shows were “woke” and “a disgrace.”

“The country, and the Kennedy Center, I gather, are in the hands of people whose ideas do not always comport with hers,” Ms. Graham’s son Don, another former publisher of The Post, said in an introductory speech.

The event, hosted by the billionaire Warren E. Buffett, a longtime friend of Ms. Graham’s, was a celebration of her life and impact. (She died in 2001 at age 84.) At times, it also felt like a wake for an era that has long since past.