What is the difference between Catholic and Protestant Bibles?
There is only one Bible, and on the whole, the Catholic and Protestant versions of the Bible are very similar. The main difference is found in the table of contents. The Catholic Bible contains 73 books of Scripture while Protestant Bibles contain 66.
The Catholic canon includes 7 Old Testament books that were not retained in the Jewish canon of scripture after the destruction of the Jerusalem Temple, specifically after the Council of Jamnia in the 2nd century AD. At that council, the rabbinical school of Pharisees in Jamnia, observing the reliance of the burgeoning Christian communities of the Greek Septuagint - a translation which was undertaken by Jewish scholars themselves in the 3rd century BC and which includes the 7 books in question - newly affirmed that the books to be held as canonical in Judaism were only those received from the Masoretic Hebrew text manuscripts. At this same council, they also rejected many of the books from what is now the Christian New Testament. The decision of a Jewish council called primarily to repudiate Christian writings is not exactly the best criteria to determine the Christian canon.
The seven OT books at issue are: Tobit, Judith, 1 Maccabees, 2 Maccabees, Wisdom of Solomon, Sirach (or Ecclesiastes), and Baruch. The Catholic Bible OT also contains some extra verses or chapters in the books of Daniel and Esther. In short, the Orthodox and Catholic Churches continue to hold the Greek Septuagint as the full canonical Old Testament while Protestants chose the Masoretic Text of the present day Jewish canon, even though these books had been regarded as canonical throughout Church history as witnessed to by the many citations made by early Church Fathers.
You can sometimes find these contested books in the Protestant Bible along with a few other bits of Hebrew Scriptures collected into a section titled "Apocrypha" usually placed between the Old and New Testaments. This explains what is meant by a Bible advertised as "with Apocrypha".