If you allow printing, there really isn't any security. Consider, for example that the user could print it, then take the stack of pages and stick it in the scanner, to scan-to-PDF.
Or, what may be a normal network printer might have a feature allowing the queued file to be viewed as PDF...
The most you can do is cause inconvenience to the uninformed or unmotivated. Who are, at least, in the majority.