PSG have been taken over by wealthy Qatari investors and the Argentine's arrival from Palermo in a reported French record 42 million euros move has made them among the favourites to win the French title this season.
They lost their opening home match 1-0 to Lorient on Saturday with Pastore in the stands but the club are ultimately aiming to become a top European force after years of underachievement.
"I came in search titles which hasn't happened up until now. That was my motivation," Pastore said on Monday in his first news conference since signing.
Inconsistent Palermo lost the Italian Cup final last season to Inter Milan, who were managed by Leonardo before the Brazilian decided to leave the three-times European champions to join ambitious PSG as sporting director.
Leonardo said Pastore, 22, had "his whole future ahead of him."
"His signing is in line with the club's policy of recruiting young, ambitious players," Leonardo added having also brought in Jeremy Menez, Salvatore Sirigu, Mohamed Sissoko, Kevin Gameiro and Blaise Matuidi.
PSG have splashed out over 80 million euros since May but coach Antoine Kombouare has been retained despite last term's fourth-place finish when modest Lille won the league and cup double.
"My team-mates had only just finished their pre-season preparations," Pastore said to explain the surprise defeat by Lorient at a packed Parc des Princes he described as having a "formidable atmosphere."
"The group is full of attacking talent and is strong at the back. We have everything in our favour to be fighting for the top positions," he added, denying it was strange to move to France from the more high-profile Italian league.
"A step backwards? No not at all. Ligue 1 is a championship that will soon be able to compete with its Italian and English rivals. It is a league which is going to improve further in terms of quality and play."
Pastore is not sure when he will be match fit to play for his new team having just come back from a two-week holiday.
"I am going to have a tough workout this week and at the end of the week I will make a first assessment to see if I can make myself available to the coach," the Argentine said.
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