This is formal written order issued by the Pope in his official capacity. It may not seem so obvious today, but five hundred years ago, the Catholic Church was the world’s first imperial superpower. Known eventually as the Holy Roman Empire, it used its spiritual control of the various subjects of Europe to oversee the conduct of the various monarchies of old Europe, who needed a Papal stamp of approval to show their subjects that their monarchies were part of their god’s will.

As a result, every European kingdom had a representative of the Pope’s government resident in its capital, with full access to the local king’s Court.
This is how the Office of the Pope came to be the one deciding which of its kingdoms would be allowed to conquer which parts of the world, at the beginning of the period of the European exploration and conquest of the world.

The Roman Empire is still recognized as an independent country, with The Pope as its head of State at the Vatican enclave located inside the city of Rome. It still maintains officially recognized ambassadors in many of the worlds capitals, and the Pope still issues Bulls.
Importantly, A Papal Bull is taken to still be in effect until the Pope in question either cancels it, or it is cancelled by a later pope either directly, or through the contents of another Bull superseding it.