Below are the English translations of the 3 founding documents for the Society of St. Pius X, of which the originals can be viewed here (in French and Latin).
The first is from the local ordinary of the diocese where Archbishop Lefebvre first opened a house of studies in Fribourg, Switzerland (where the seminarians were attending the still-conservative diocesan University of Fribourg).
The second is the Fribourg's bishop's approval of the SSPX's Statutes composed by Archbishop Lefebvre, and thus permission to erect the Priestly Society of St. Pius X as a pious union of priests in the diocese, originally for an experimental period as is customary with newly-established religious congregations.
The third is the canonical approval from the Holy See (the Congregation of the Clergy) for the erection of the Society of St. Pius X. This permanently established the pious union of priests founded by Archbishop Lefebvre as an official religious congregation of the Roman Catholic Church.
That the experimental period had not even been concluded before this important step was achieved, demonstrates the great Providence of God that Archbishop Lefebvre always relied upon to ensure the survival of Tradition—particularly in hindsight of its forthcoming persecution in just a few short years' time.
To get a better perspective of the historical context of these important events, see:
By these presents, We, Francois Charriere, Bishop Lausanne, Geneva and Fribourg, confirm the authorization which We gave to His Excellency Archbishop Marcel Lefebvre, in an audience on June 6, 1969; to open at Fribourg an international house for candidates for the priesthood who will study at the University.
We implore for these future priests and on those who oversee their formation the blessings of Almighty God.
At our bishop’s residence in Fribourg, August 18, 1970
[signed] + Francois Charriere, Bishop of Lausanne, Geneva and Fribourg
Given the encouragements expressed by the Second Vatican Council, in the decree Optatum Totius, concerning international seminaries and the distribution of the clergy;
Given the urgent necessity for the formation of zealous and generous priests conforming to the directives of the cited decree;
Confirming that the Statutes of the Priestly Society correspond to its goals:
We, Francois Charriere, Bishop of Lausanne, Geneva and Fribourg, in the Holy Name of God invoked and all canonical prescriptions observed, decree what follows:
We implore divine blessings on this Priestly Society that it may attain its principal goal which the formation of holy priests.
Given at Fribourg, at our episcopal residence.
November 1, 1970, on the Feast of All Saints,
[signed] + Francois Charriere,
Bishop of Lausanne, Geneva and Fribourg
Sacred Congregation for the Clergy
February 18, 1971
Prot. N. 133515/I.
Exc. me Domine [Excellentissime Domine],
With great joy I received your letter, in which your Excellency informs me of your news and especially of the Statutes of the Priestly Society.
As Your Excellency explains, this Association, which by your action, received on 1 November 1970, the approbation of His Excellency Francois Charriere, Bishop of Fribourg, has already exceeded the frontiers of Switzerland, and several Ordinaries in different parts of the world praise and approve it. All of this and especially the wisdom of the norms which direct and govern this Association give much reason to hope for its success.
As for the Sacred Congregation, the Priestly Society will certainly be able to conform to the end proposed by the Council [for the formation of seminarians], for the distribution of the clergy in the world.
I am respectfully, Your Excellency,
Yours in the Lord.
addictissimus in Domino,
J Card. Wright, Praef.
Exc.mo ac Rev.mo Domino
D.no Marcello LEFEBVRE
Archiepiscopo tit.de Synnada in Phrygia
Via Casalmonferrato, n. 33