The Apostille is a formality to certify the authenticity of the public acts issued in a State to take effect in another one giving those documents a formal probationary importance; this formality is needed for the signatory countries to the 05/10/1961 Hague Convention Abolishing the Requirement for Legalization for Foreign Public Documents.
Which documents need apostille
All acts issued by the notary’s offices, registration offices, courts, ministries, town halls, local administration offices and schools need an apostille.
The central responsible authority in Portugal to issue and verify apostilles is the Procurador-Geral da República; that responsibility is extended to the Procurador-Geral da República in Oporto, Coimbra and Évora and to the Public Prosecution magistrates ruling the offices in Funchal and Ponta Delgada.
Find some more information in the Public Prosecution portal