Almost everyone who becomes a fiscal resident in Portugal will not pay taxes on their pension. But there are certain exceptions such as citizens with residency in tax havens or countries like Sweden which withdrew from the tax convention with Portugal.
From the moment you become a Portuguese tax resident, it is up to the Portuguese government to tax your pension. For the first 10 years the Portuguese government will tax you 0% (ZERO) on your pension income. You can also be exempt from paying taxes on your dividends, capital gains taxes, royalties and real estate rent income. You are exempt from inheritance taxes.