Pope Francis signed a new encyclical called "Fratelli tutti" (All Brothers) in the Italian town of Assisi on Saturday, his first trip outside Rome since the coronavirus pandemic erupted.
An encyclical is a letter containing an important teaching that is circulated by the pope to the Church.
It is the pope's third encyclical, and is about brotherhood in the world and social cohesion. The text is also expected to touch on the crisis unleashed by the coronavirus, and its consequences.
According to the news agency Ansa, the pope traveled to the town in the Umbria region by car, and waved to onlookers during his journey.
He also stopped to visit the convent of Poor Clares of Vallegloria in Spello, Ansa reported.
Before signing the encyclical, the pope first celebrated Mass at the tomb of St. Francis, attended by 20 people including Cardinal Agostino Vallini. Most of the worshippers wore protective face masks.
He was expected to return to the Vatican in the evening.
More is not yet known about the contents of the encyclical, which was set to be released by the Vatican on Sunday.
In reference to the encyclical, the pontiff tweeted on Saturday: "The effort to build a more just society implies the capacity of fraternity, a spirit of human communion."
The document's importance was underlined by the fact that the pope travelled to the city where Saint Francis, the medieval monk famous for his love of nature, was born.
Born Jorge Mario Bergoglio, 83-year-old Pope Francis was the first pontiff to name himself after the monk, known for his poverty vows, love of nature and rejection of violence.
Assisi is home to St. Francis' Basilica, one of the world's most important Catholic places of worship, hosting the burial chamber of the medieval monk. It is a UNESCO World Heritage site.
Pope Francis' two earlier encyclicals were "Lumen fidei" (Light of Faith) in 2013, and "Laudato si" (On the Care of the Common House) in 2015. The latter, addressing the environment, was seen as a global clarion call to underline the need for climate protection and to combat poverty.