Though they are U.S. citizens, Puerto Rican citizens cannot cast votes in U.S. presidential elections. They can vote in a presidential primary, and they send delegates to the political conventions. The same is true for the other U.S. territories of Guam, American Samoa and the Virgin Islands.
Puerto Rico does not have any delegates in the Electoral College. The Constitution specifically states that only states and the District of Columbia are allowed to send electors. U.S. citizens who are registered to vote in the United States but are living in Puerto Rico may vote by absentee ballot in the election if they wish.