It looks like the "user canceled print" message may be triggered when the PDF cannot be created at the specified location. 

In ProSeries go to Print and click the "Printer, PDF, and DMS Setup" button.  Look at the "PDF Files" section of the setup window (top right) and review the "path" specified right above the Browse button.  You may find something unusual with this path statement, like a drive that no longer exists, extra slash, a folder that has been deleted, etc. If the path points to a location that does not exist, this will be the problem.

To resolve the problem, click the Browse button and navigate to the folder that will store PDF files when they are created (the destination).  When ProSeries is not installed on a network, this location is usually C:\ProPDF\TY2018, but you can specify any folder you want.  After navigating to your preferred destination, click OK to save the change and close the Browse window. 

Now try emailing a password protected PDF to see if the error is resolved.