If you are a resident in Portugal and holder of a driver’s license issued by another country, at some point you have to swap your old license for a Portuguese one. Timing and process depend on where your license was issued.
IMT I.P. (Instituto da Mobilidade e dos Transportes) have detailed instructions in English online. As rules seem to be changing frequently lately, best look for the latest info here:
http://www.imtonline.pt/index.php/troca-de-titulos-conducao-estrangeiros/driving-licence-exchange109
The process is different depending on where your current license was issued.
EU: You can drive in Portugal on an EU driving licence until it expires.You must register your address in Portugal with IMT services within 60 days of settling in Portugal. There is no charge for this service.
Special categories
If your license includes heavy vehicles or large trailers, you will have to take a “CAP” (psychological suitability test that I gather mainly checks reflexes) and submit the certificate with your application. However, there have been instances where people have been denied the additional categories despite having done the CAP. This seems to relate to whether a specific test was passed to obtain those categories, i.e. older licenses that included other categories after having passed merely a test for passenger cars appear to lose the extra categories upon exchange. The water is muddy on this, so investigate in good time.