Sr Lucia dos Santos was 10 years old in 1917 when the Blessed Virgin Mary reportedly appeared to her and to two young cousins, on the 13th of each month, from May to October of that year. The "third secret" was only revealed on 13 May 2000.
The manuscript will be on loan from the Vatican.
Fátima has since become one of the leading Marian shrines in the world, drawing millions of pilgrims every year, from all over the world, including every pope since Paul VI, who came in 1967.
Some interpreted the "third secret" as having foretold the attempted assassination of Pope John Paul II, which occurred on 13 May 1981 in St Peter's Square. It mentions the murder of "a bishop dressed in white - we had the impression that it was the Holy Father".
John Paul II attributed his survival to the intervention of the Virgin of Fátima. However, the then-Cardianal Ratzinger wrote a theological interpretation of the secret in which he stated: "A careful reading of the text of the so-called third 'secret' of Fatima (...) will probably prove disappointing or surprising after all the speculation it has stirred. No great mystery is
revealed; nor is the future unveiled." He said instead "the vision speaks of dangers and how we might be saved from them".