The Apocrypha or Deuterocanonical books are a group of books written after the principal books of the Old Testament and the New Testament were finished. Most scholars do not believe they belong in the Bible. Unger's Bible Dictionary has a good explanation of why these books should not be considered to be Scripture.
"Old Testament Apocrypha. In its final quasi-technical meaning of ‘noncanonical,' in common use since the Reformation, the term specifically refers to the fourteen books written after the OT canon was closed and which, being the least remote from the canonical books, laid strongest claim to canonicity. The OT apocryphal books…have been rejected as inspired for the following reasons:
"1. They abound in historical and geographical inaccuracies and anachronisms.
"2. They teach doctrines that are false and foster practices…at variance with inspired Scripture.
"3. They resort to literary types and display an artificiality of subject matter and styling out of keeping with inspired Scripture.
"4. They lack the distinctive elements that give genuine Scripture its divine character, such as prophetic power and poetic and religious feeling.
"New Testament Apocrypha. The apocryphal books of the NT, unlike those of the OT, have never claimed the faith of the Christian church, except in a few isolated instances. There are more than one hundred of them, and it is doubtful whether one of them appeared before the second century of our era. Most of them portray a much later date. They are valuable as an indication of the growth of thought and the rise of heresy in the age just subsequent to that of the apostles. None of them ever received the sanction of any ecclesiastical council" (1988, "Apocrypha").
Jesus said "the Scripture cannot be broken" (John 10:35), which means that genuine Scripture consistently agrees with itself throughout. Since these books are filled with inaccuracies and disagree with the plain teachings of the Bible, they could not be a part of God's Word.
Jesus also affirmed the three sections of the Hebrew Scriptures preserved and accepted by the Jews. He said, "All things must be fulfilled which were written in the Law of Moses and the Prophets and the Psalms concerning Me" (Luke 24:44). The apostle Paul explained that God committed to the Jews "the oracles of God" (Romans 3:2). The Jews did not accept the Apocrypha, and so neither did the Church.
For more information, please read our free booklet, "Is the Bible True?"