The Autoridade Tributária e Aduaneira, commonly referred to as Finanças, is the Portuguese tax and customs authority.
Offices exist in all towns, the nearest to Monsanto is in the Camara of Idanha-a-Nova, entrance on the side.
Like all public service entities, they are encouraging online interaction during the Covid pandemic, and attendance in person is only by appointment.
Tel. 277 200 510
e-mail: sf0639@at.gov.pt
Some information is available in English here
Portal das Finanças
If you already have a NIF, you can handle your tax issues online, after a registration process:
1-2 weeks after registering as a new user on the above site, you will receive a letter by snail mail with your access code to https://www.portaldasfinancas.gov.pt/
There, you can find e.g. reference numbers to pay car tax through multibanco, see if any other taxes like property tax are due, and if you pay income tax, there are some nifty tools to administer deductible expenses and submit income tax returns.
- e-Balcão (Portal das Finanças): https://www.portaldasfinancas.gov.pt/pt/formularioContacto.action
- Centro de Atendimento Telefónico: 217 206 707
NIF
If you are planning to buy property in Portugal and/or become a resident, you need to register with Finanças to obtain your Número de Identificação Fiscal or NIF.
If you don’t have a NIF yet, call Centro de Atendimento Telefónico: 217 206 707 or make an appointment at local Financas office.
All links I’ve found so far to apply for a NIF online start by having to enter your NIF 🙁
I’ll update here if & when I find out something more useful.