Has the Pope got the authority to pronounce (declare) a person as Saint?
Yes, Pope is the rightful successor of Peter whom Christ has appointed the Supreme Authority of the visible church. The promise to Peter, that "I will give you the key of the Kingdom of Heaven, and whatever you bind on earth will be bound in Heaven, and whatever you loose on earth will be loosed in Heaven, holds good to the Pope also. So he can pronounce a person as a Saint. Moreover it is rewarding that some of the members who have led heroic Christian life be exacted as exemplary for the benefit of others. In NT, Job (James 5:11) and Abraham (Heb. 11 :8) are cited as examples of patient suffering and deep faith. Exalting a few doesn't mean that others are unholy. Each christian is called to be holy (Mt. 5 :48; 1 Cor 1 :2), and rightly all the early christians were called "Saints" (1 Cor. 1 :2,24; Rom 1 :7). Hence it is our bounden duty to become saints, whether we are officially declared or not. (1 Pet. 2:5).