The former Napoli forward moved to Parc des Princes for a fee believed to be in the region of €30 million (£23.7m), following in the footsteps of his compatriot, who took the well-trodden path from Serie A to the French capital 12 months earlier.
And Pastore, who arrived from Palermo, is delighted that his club have signed such a high-profile player, and is excited to play alongside the former Estudiantes forward.
"I'm very happy with his arrival because he is a friend of mine," he told the club's official website.
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"I got to know him in the national team, and his coming here has made me very happy. It's certain that he will bring us a lot going forward, and that is decisive for us.
"We know that he has great potential and that he will be an added asset to us."
Paris Saint-Germain finished second in last season's Ligue 1 table, just three points behind surprise winners Montpellier.