Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
IRS Annex J: Declaring Foreign Income
If you are a tax resident in Portugal (like most D7/D8 holders), you must declare your worldwide income, not just what you earn locally. This is done in "Annex J" of your annual tax return.
You must list pensions, dividends, and salaries earned abroad. Even if this income is not taxed in Portugal due to Double Taxation Treaties, failing to declare it is tax evasion and carries heavy fines.