Pensions are considered income from employment. ( Art.12.2.c IRPF )
Benefits for retirement subject to Personal Income Tax are both those received
from public entities and those received from private entities, resulting from the taxpayer’s savings.
Remember that pensions are general income and that there is a 24000 € allowance on General income.
Taxes paid abroad can be credited.
A double tax treaty may reduce your taxation.
A pension paid as a result of your spouse´s occupation might be considered as savings income.