No, you cannot take up paid employment while on a Portugal Jobseeker Visa until you have secured a formal job offer and changed your visa status to a residence permit that allows work. The visa is intended solely for job hunting and attending interviews. Once you receive a valid work contract that meets Portuguese labour laws, you can apply at the Serviço de Estrangeiros e Fronteiras (SEF) to switch to a work-based residence permit or EU Blue Card, which will then allow you to live and work in Portugal legally.