There are many areas where you must use the number such as:
1.Purchase and sale of a property.
2.Inheriting Portuguese assets in a last will and testament.
3.Opening a bank account.
4.Getting loans (e.g., getting a mortgage, signing a mobile phone contract).
5.Paying taxes in Portugal.
6.Receiving an income for business/work.
7.Attending a local university.
8.Receiving social security payments.
9.Setting up telecommunications or utilities.
10.Purchase of a car, or application of a driving license.
11.Signing a mobile phone contract.
12.And most other fiscal activities.