Is it obligatory to pound the pages of the Mushaf after burning them, or is it permissible to dispose of them, and are the letters that appear on the burnt pages real letters?

If a Mushaf (copy of the Quran) cannot be used due to fear of desecration, it is permissible to burn it, as Uthman ibn Affan did. This is on condition that the letters are completely removed after burning, by pulverizing the papers until they become ash, or at least until the image of the letters disappears. If they do not disappear by burning, then they must be crushed or torn into very fine pieces until no image of the letter remains.