§1. Even if documents are common, no one is bound to present those which cannot be communicated without danger of harm according to the norm of can. 1548, §2, n. 2 or without danger of violating an obligation to observe secrecy.
§2. Nonetheless, if at least some small part of a document can be transcribed and presented in copy without the above-mentioned disadvantages, the judge can decree that it be produced.
Source: Code of Canon Law (Vatican.va)