I sell PDF downloads on the topic of how to play musical instruments.
You can see an example here:
[url removed, login to view]
My problem is that teachers will download the book and make copies to give to their students.
This is OK for one batch of students, but I want a method of controlling how many students can get copies.
I'm thinking of a password controller, that prevents the PDF from being opened more than a certain number of times, or a password that expires after a set time.
I know that PDFs can be saved with a requirement that the user must enter a password, but that password can be shared and lasts indefinitely.
Is there any way to control the behavior of the password?