It may be a first in the annals of government secrecy: Declassifying documents to mark the anniversary of their leak to the press. But that is what will happen Monday, when the federal government plans to finally release the secret government study of the Vietnam War known as the Pentagon Papers 40 years after it was first published by The New York Times.

At first blush, it sounds like the release of one of the worst-kept secrets in history — finally unlocking the barn door four decades after the horses bolted. The study, after all, has already been published by The Times and other newspapers, resulting in a landmark First Amendment decision by the Supreme Court. It has been released in book form more than once. But it turns out that those texts have been incomplete: When all 7,000 pages are released Monday, officials say, the study can finally be read in its original form.

That it took until the era of WikiLeaks for the government to declassify the Pentagon Papers struck some participants as, to say the least, curious.

“It’s absurd,” said Daniel Ellsberg, the former RAND Corporation analyst who worked on the report and later provided it to The Times. He said Tuesday that the report should not have been secret even in 1971, when newspapers first published it, adding: “The reasons are very clearly domestic political reasons, not national security at all. The reasons for the prolonged secrecy are to conceal the fact that so much of the policy making doesn’t bear public examination. It’s embarrassing, or even incriminating.”