Download file with password and paypal

I have this file for download that is password protected.
If the user pay it by Credit Card (off line transaction) or Check, the CC or check need to clear before I send the user a password to open the file.
But if the user pay using Paypal, I would like to make that the user receive an e-mail with the password automatic.
Is there any way to do that?
Many users buy via Paypal, and they get frustrated when they cannot open the PDF right away.

Thank you
ehm

As you know, customers cannot access the file if they haven't paid for it, thus simply the fact of being paid or not is automatically handling authorized access to a large extent.
What is the reason for password-protecting the file on top of that?

DrByte:

As you know, customers cannot access the file if they haven't paid for it, thus simply the fact of being paid or not is automatically handling authorized access to a large extent.
What is the reason for password-protecting the file on top of that?

I may be wrong, but would be possible to a 'smart' user to point his/her browser to the download path on zen cart and 'grab' the files from there?

Sure, if you don't do anything to prevent that.
But, if your server supports Download by Redirect, then you can protect it this way: https://www.zen-cart.com/tutorials/index.php?article=280