When Adam was placed on this earth all his former knowledge was taken away. Yet the Lord has made known to us that Adam lived before and had experiences as Michael, the great prince, who was chosen to stand at the head of the human family on this earth as the Ancient of Days.
Joseph Fielding Smith, The Way to Perfection, p.17
What is wrong with this picture?
Firstly, the Bible plainly says we exist physically before we exist spiritually (1 Cor. 15:44-46) so there was no “former knowledge” for Adam to have. Secondly, Adam was a man while Michael was an angel - two different types of created beings. Lastly, the “Ancient of Days” spoken of in Daniel 7 is God. God created Adam, so the two cannot be the same. However, this citation harks back to the Adam-God doctrine taught by Brigham Young and denied by the LDS today.