
Hi @imthemanadrian ,
I hope you've sold a lot of books and found a solution not to insert watermarks manually. If you're doing this manually, Plumsail Documents could be a game changer for you. In this how-to guide, there is a case you exactly mentioned - apply watermarks with recipient's email address dynamically - https://plumsail.com/docs/documents/v1.x/flow/how-tos/documents/add-a-text-watermark-to-a-PDF-document.html
Note: this is a paid solution. But a free trial along with custom pricing are available.