Section — Wouters, Manual of Moral Theology
Section III. On the Papal or Apostolic Blessing
I. Notion. A papal blessing is a blessing granted by the Supreme Pontiff or in his name. It is a sacramental, to which a plenary indulgence is usually attached.
II. Granting of the blessing.
Who can grant it by common law, see n. 494.
In granting the blessing the prescribed formula is to be used (canon 914). Moreover: 1. Bishops and other secular Prelates are to use the rites and formula prescribed by Clement XIII, September 5, 1762, and inserted in the appendix of the Roman Pontifical. 2. Regular Prelates are to use the formula established by Benedict XIV through the Encyclical Exemptis praedecessorum, March 19, 1748, and reported in the Roman Ritual, title VIII, chapter 32. 3. Missionaries can grant it with the sign of the Cross alone and the formula: "May the blessing of Almighty God, Father, and Son, and Holy Spirit, descend upon you and remain always. R. Amen";1 nevertheless it is permitted to use the formula of the Roman Ritual.
1 Sacred Congregation of Rites, May 11, 1911, to III.
III. Acquisition of the indulgence. Unless something else is expressly established, for acquiring the indulgence it suffices that one be: 1. present to the one blessing; 2. contrite in heart, or in the state of grace.1
1 Cf. Fanfani, p. 74.