How to prevent Duplicate Purchase Order to be sent to Supplier?

Summary:

We are creating custom template for Purchase Order PDF and sending the same to the Supplier using the Email available at PPO Header. Buyers have the ability to click on View PDF and download it and send it as well. This can result in duplicity of same PO Document with the Supplier. Can this be prevented?

Content (required):

Open PO , then View PDF, Custom PO PDF is available.

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):