My buddy and I noticed recently that in all the hours and hours of fishing we both have done, we're able to find Protection, Fire Protection and Blast Protection books, but there's not a single Projectile Protection book to be found. I know it hasn't been completely removed since I can see the book when I go in creative. Has this been removed in book form in survival and only available from an enchanting table now? We were thinking it would come in handy when we're hunting mobs in our pyramid as there's often times we're facing 10 plus skeletons at once....
According to the following calculator it is possible to get Projectile Protection on a book but it is extremely rare (0.2% of any level) at level 30 (the level books obtained from fishing are enchanted at); however, it is much more likely at lower levels (level 15 gives a 4.2% chance, slightly lower than Fire Protection and higher than Blast Protection, This suggests that the ideal level for Projectile Protection is lower; it is obtainable with a lower enchantment "power" but becomes displaced by other enchantments at higher levels as the "power" becomes too high to choose even level IV):
While it doesn't let you view the probabilities for individual enchantments on books, only tool and armor, the following chart for an iron helmet shows that the probability of Projectile Protection falls to near zero by level 30 (as mentioned above, the enchantment "power" can become too high, with each level of an enchantment having a certain level it peaks at with the probability decreasing on either side):
For comparison, the probability of Fire Protection IV is still increasing at level 30, but it would too eventually start to decrease (this suggests that at a high enough level you wouldn't be able to get any enchantments):