The enchanted scroll is an item obtained from Veos during the Client of Kourend quest. A feather must be used on it to obtain an enchanted quill.
When written on this quill, the client will see what the player is writing without anything being seen on the scroll itself. When the player asks Veos if they are spying for the client, he will say that he wishes to keep this task on the down low. It is possible to create a duplicate by banking the first scroll and asking Veos for a replacement, but upon the quest task being completed the duplicate will be removed from one's inventory or bank.