The Vatican has been trying for years to debunk the idea that its vaunted secret archives are all that secret: It has opened up the files of controversial World War II-era Pope Pius XII to scholars and changed the official name to remove the word “Secret” from its title. The longtime prefect of what is now named the Vatican Apostolic Archive, Archbishop Sergio Pagano, is spilling the beans for the first time, revealing some of the secrets he has uncovered in the 45 years he has worked in one of the world’s most important, and unusual, repositories of documents. In a new book-length interview titled “Secretum” to be published Tuesday, Pagano divulges some of the unknown, lesser-known and behind-the-scenes details of well-known sagas of the Holy See and its relations with the outside world over the past 12 centuries.