The project to build the Baltic Pipe pipeline is part of Warsaw’s efforts to diversify gas supplies and reduce the country’s energy dependence on Russia.
Construction of the pipeline, which will connect Poland with Norway via Denmark, is due to start next year.
Duda on Monday described it as "a strategic project for Poland’s energy transformation, as well as for the energy security of the entire Central and Eastern Europe region."
He added that Polish and Danish investment in offshore wind energy could spur a "green transformation" in the region.
The Danish royal couple were in Poland on a one-day visit as the two countries mark 100 years of renewed bilateral relations.
Duda and First Lady Agata Kornhauser-Duda welcomed Denmark’s Crown Prince Frederik and Princess Mary in a ceremony at the Presidential Palace in Warsaw before noon.
Duda and Prince Frederik were scheduled to attend debates on energy cooperation and clean air at Warsaw’s Bristol Hotel.
Warsaw and Copenhagen renewed diplomatic relations after Poland in 1918 regained independence in the wake of World War I, following 123 years of partition by Russia, Austria and Prussia.