The Portuguese tax authorities published a guide to VAT for non-resident taxpayers doing business in Portugal.
The non-resident taxpayers covered by this guide are companies that do not have their registered office, permanent establishment or domicile in the Portuguese national territory and that have an economic activity in the territory.
Are you in this situation and would like information on your VAT obligations? You can consult the FAQ of the administration(here) or our country file Portugal(here).