Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
NIF: The First Document You Need
The NIF (Número de Identificação Fiscal) is your tax ID. You cannot open a bank account, rent an apartment, or sign up for internet without it. It is the absolute foundation of your move.
You can obtain one remotely through a fiscal representative (lawyer or company) before you arrive. Do not wait until your visa appointment to sort this out; have it ready early.