This journal documents all observations made by Plik in his years of running his safari. When read, it grants the Ghoul Ecology perk. Plik's journal uses the world model of the sheet music book. The placement in game covers up any musical notes though, so this is not noticeable. Activating the journal will cause the player to do +5 damage to ghouls.
It cannot be picked up without use of the console, but it is classified as a quest item and as such cannot be dropped once in your inventory.