Frank Grevil, a former intelligence officer, was previously imprisoned for leaking the documents in the case, which was viewed in Denmark as a landmark test of media freedom.
Lunde called the verdict "a great victory for the open society".
Prosecutor Michael Joergensen said he had not yet decided whether to appeal.
During the trial, which began on November 13, the prosecutor claimed that the newspaper, one of Denmark's largest circulated dailies, violated a law that prohibits media from publishing classified information that could harm national security.
Joergensen had recommended that each of the defendants be given a four-month prison term - the same sentence given to Grevil after he was convicted last year of leaking the documents to the reporters.
In Monday's ruling, Judge Peter Lind Larsen said the "considerable public interest" in the information outweighed the government's concerns that its intelligence-gathering operations were jeopardised.
Press freedom advocates welcomed the decision, which was met with applause in the packed court room.