Primo Feliciter was a motu proprio issued by Pope Pius XII on March 12, 1948.The Church in the Modern Age (Vol 10) by Hubert Jedin, Gabriel Adriányi, John Dolan , Hypeion Press p. 327.
Primo Feliciter was issued a year after the constitution Provida Mater Ecclesia. This motu proprio confirmed and blessed secular institutes within the Catholic Church.
Along with Provida Mater Ecclesia and Cum Sanctissimus, Primo Feliciter provided the basis for Catholic secular institutes to receive their own legislation.Christian Spirituality in the Catholic Tradition by Jordan Aumann 1985 p. 272.
Notes
References Primo Feliciter at the Vatican website