Chapter — Wouters, Manual of Moral Theology
Chapter III. On Exemption from the Prohibiting Law, and on Permission to Use Prohibited Books
I. Those who in any way devote themselves to theological or biblical studies can use even prohibited texts and versions of Sacred Scripture, provided the said texts and versions have been published faithfully and integrally, and the dogmas of the Catholic faith are not attacked in their prolegomena or annotations (can. 1400). It is said:
Those who... in any way devote themselves, i.e. both clerics and laymen who not merely incidentally or passingly, but habitually for some time, are especially intent upon those studies.
Dogmas of the Catholic faith; under this name do not come other truths, however theologically certain.
II. Cardinals of the Holy Roman Church, Bishops, even titular Bishops, and other Ordinaries, with the necessary precautions employed, are not bound by the ecclesiastical prohibition of books (can. 1401).
III. With respect to the faculty of granting permission, note: the following can grant it:
The Supreme Pontiff, who grants it through the Holy Office (can. 247, § 4). Yet those who have obtained an apostolic faculty of reading and retaining prohibited books cannot therefore read and retain any books whatever proscribed by their Ordinaries, unless in the apostolic indult the power of reading and retaining books condemned by anyone whatever has been expressly given to them (can. 1403, § 1).
Ordinaries, namely both local Ordinaries and major Superiors of an exempt clerical religion, are able, with respect to books prohibited by the law itself or by decree of the Apostolic See, to grant permission to their subjects only for individual books and only in urgent cases (can. 1402, § 1). But if they have obtained from the Apostolic See a general faculty of permitting their subjects to retain and read proscribed books, they should grant it only with choice and for a just and reasonable cause (can. 1402, § 2).
Note that local Ordinaries can also grant to subjects permission, but only in particular cases and for a just cause, to use books prohibited by a plenary or provincial Council (can. 82; 291, § 2).
The petition by which permission is sought must be recommended by the local Ordinary if there is question of a secular cleric, and by his own Superior if there is question of a religious. For a layman, generally the recommendation of the confessor suffices.
IV. With respect to permission granted, observe:
Those who have obtained permission are held by a grave precept to guard prohibited books in such a way that they do not come into the hands of others (can. 1403, § 2).
Permission obtained from anyone in no way exempts a person from the prohibition of natural law against reading books which present a proximate spiritual danger to him (can. 1405, § 1).
Add the warning of the Code: Local Ordinaries and others having care of souls should opportunely warn the faithful concerning the danger and harm of reading bad books, especially prohibited books (can. 1405, § 2).