Hello ftselec, and welcome to the Forums!
You should be able to create a "WATERMARK" layer, make the text cover the whole drawing, say from corner to corner, then set the transparency to 50%, and lock the layer.
Then when the PDF is created, it will always show the watermark, and if they want the drawing without it, they have to purchase it from you.
Of course, once that drawing is printed, it could get into unwanted hands, but at that point you would probably be able to track who had access to the unmarked drawing.
Additionally, there are security measures that can be set on the PDF itself.
Here is what the HELP file has to say about security:
"About Passwords and Encryption
Current security requirements are increasing due to the nature and sophistication of the threats encountered online.
Beginning with AutoCAD 2016-based products, the ability to add passwords to drawing files was removed. Instead, we recommend that you purchase an encryption product that meets current industry standards and is updated as needed. For AES symmetric encryption, security experts currently recommend the 256-bit protocol. For RSA asymmetric encryption, they usually recommend the 2048-bit protocol as the minimum for general security and the 4096-bit protocol for internet transactions.
It is recommended that you consider one of the following alternatives to protect drawing files that contain sensitive information:
Output the drawing as a PDF file, and add a password to the PDF
Package the drawing in a ZIP file, and add a password with a secure external utility
Use a third-party password and encryption utility with, for example, 256-bit AES technology or equivalent
Protect the drawing behind network permissions
Protect the drawing behind Autodesk 360 or other cloud provider permissions"
and
"Commands for Protecting and Signing Drawings
Commands
DIGITALSIGN (Command)
SAVEAS (Command)
SECURITYOPTIONS (Command)
SIGVALIDATE (Command)
System Variables
SIGWARN (System Variable)"
I hope that helps.
If you have any more questions about this topic, or the information I posted, please feel free to post back and I will be happy to assist you!
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Steve Tamplen
Technical Support Specialist