In what way did Daniel seal the words of the scroll in Daniel 12:4?
I will have to say I really am not sure that Daniel DID anything. I will be honest that I have not really thought all that much about the meaning of this passage. I have not seen any deep, hidden or symbolic meaning here. I have always just gone with what I thought was the “obvious,” which is that God is telling Daniel that this is the end of the prophecies that he will be receiving, and therefore, this marks the end of what would eventually be the book that we call Daniel. Interestingly, in the Apocrypha, there are “additions to Daniel” which were almost certainly written at a much later date. Perhaps God was wanting to give us a hint that we should ignore any “additions” to the book.
It is worth noting in this connection that in the prophecy in Daniel 9:24 it is said that at the end of the seventy weeks, after the time of the Messiah and the destruction of Jerusalem (in AD 70) that vision and prophecy will be “sealed up.” I believe that this, too, is an indication that God will in a sense bring the end to new inspired prophecy around the time of the destruction of Jerusalem. If I understand the Bible correctly, with the book of Revelation–written within less than a generation of the destruction of Jerusalem, biblical revelation came to an end.