Portugal: double taxation agreement, Article 25: Exchange of information
(1) The competent authorities of the Contracting States shall exchange such information as is necessary for the carrying out of this Convention and of the domestic laws of the Contracting States concerning taxes covered by this Convention insofar as the taxation thereunder is in accordance with this Convention. Any information so exchanged shall be treated as secret and shall not be disclosed to any persons or authorities other than those (including a court or administrative body) concerned with the assessment or collection of, or prosecution in respect of, or the determination of appeals in relation to, the taxes which are the subject of the Convention.
(2) In no case shall the provisions of paragraph (1) be construed so as to impose on one of the Contracting States the obligation:
(a) to carry out administrative measures at variance with the laws or the administrative practice of that or of the other Contracting State;
(b) to supply particulars which are not obtainable under the laws or in the normal course of the administration of that or of the other Contracting State;
(c) to supply information which would disclose any trade, business, industrial commercial or professional secret or trade process, or information, the disclosure of which would be contrary to public policy (ordre public).
(3) The competent authorities of the Contracting States shall notify to each other any changes which have been made in their respective taxation laws.