VATICAN CITY (Reuters) -Pope Leo urged the world's Catholics to help immigrants in his first major document, which was released on Thursday and invoked one of the late Pope Francis' strongest criticisms of U.S. President Donald Trump's anti-immigration policies.Leo's document, known as an apostolic exhortation, is focused on the needs of the world's poor. It calls for widespread changes to the global market system to address rising inequality and to help people living paycheck-to-paycheck.The 104-page text started as a writing project by Francis, who was unable to complete it before his death in April after 12 years leading the global...