For a Portuguese nationality application, the Brazilian birth certificate has to be the full-text version (certidão de inteiro teor). The version most people keep at home is the short one, and it does not work. The full-text certificate reproduces the complete entry in the registry book, with every annotation: recognition of paternity, change of name, the parents' divorce. That complete content is what the IRN reads to check the family chain.
The practical reason is simple. The IRN needs to see each annotation to follow the line of descent. A short certificate can leave out exactly the detail that proves the relationship. Ordering the wrong document at the registry office and finding out later costs time.
On the child path, you need the full-text certificate of your own birth and that of the Portuguese parent. On the grandchild path, the chain needs three birth records: yours, the one of the parent who forms the middle link, and the birth record (assento) of the grandparent. That last one comes from Portugal, not Brazil.
The Hague apostille
Every Brazilian document going to Portugal needs a Hague apostille. The apostille is a certification attached to the original document. It proves that the registry office's signature and seal are genuine, without consular legalization. Portugal is a party to the Hague Convention, so the system works directly between the two countries.
The Brazilian documents that need an apostille are the applicant's birth certificate and the parent's certificate, when it was issued in Brazil. If the parents' marriage certificate is needed to explain a change of surname, it needs an apostille too.
How to get the apostille in Brazil
You can get the apostille at any registry office (cartório) accredited by the CNJ, wherever the record was made. You do not have to go back to the office in your home town. The CNJ keeps the list of accredited offices on its website. If you live in São Paulo and the record is from Recife, you can get the apostille in São Paulo.
Bring the original document or a certified copy. The apostille is usually ready the same day or within two working days, depending on the office. It comes attached to the document or printed on the back, with a verification code.
The Portuguese birth record needs no apostille
The grandparent's birth record, issued by a Portuguese civil registry office (conservatória) or a District Archive, is a Portuguese public document. It does not need an apostille for a nationality application in Portugal.
How long the apostilled certificate is valid
The apostille itself does not expire. The apostilled certificate can. Registry offices may require the certificate to be recent. Check the exact period at irn.justica.gov.pt before ordering, so you do not have to renew later.
Mariana, from Belo Horizonte, the granddaughter of a man from Braga, ordered her own birth certificate and her mother's in full-text form at her local registry office. The same day, she had both apostilled at the counter. Her grandfather was born in 1942, so she ordered his birth record directly through the IRN's Civil Online in Portugal.
Linha Reta drafts the declaration of intent and the complete list of documents for your case. You order the records in Brazil and in Portugal, get the apostilles, and file the package with the IRN.