Buying property as a US citizen
For American buyers, appointing a fiscal representative in Portugal is, as a rule, required for relevant tax purposes when you are not tax-resident in the EU or EEA. You will also need a Portuguese NIF (tax identification number), and a power of attorney with the correct scope if you do not travel for every act. Documents executed in the United States may need notarial certification or a Hague apostille.
Before committing to a seller, due diligence on the land registry, burdens, licensing and tax documentation is advisable — distance should not mean skipping these checks.