The second attachment is the full text of the letter Joseph wrote from Liberty. D&C 121-123 was taken from the very large letter written by Joseph Smith a few weeks before the group escaped. Although the two part letter was written in 1839, it was not until the 1876 edition of the Doctrine & Covenants that it was included. Brigham Young had instructed Orson Pratt to take selections of the letter to be made into what is now known as Sections 121-123.
Of the 7,420 word letter, only 33% is found in the Doctrine & Covenants. The rest of the letter contains humor, reflections, and wonderful teachings from Joseph about conversion, persecution, leadership, correction, friendship, government, and more. What I have highlighted in YELLOW is what is found in our D&C today.
I like to tape the letter together and have the class see the whole text so they can see it is only a portion that we have in the Doctrine & Covenants.