Annotate PDF - creating a student version

Hi all

I have Moodle 2.7.

I have successfully annotated a PDF.  When I close the annotations they save ok and are still there when I load up.

How do I create a student version of the PDF with annotation so that they can see it?

I notice when I "save" the grading page an error occurs

"Can not read file, either file does not exist or there are permission problems

More information about this error"

Finally, this link:

https://moodle.org/plugins/view.php?plugin=assignsubmission_pdf

suggests there should be a "Generate Reponse" button - which I can't find anywhere.

Any advice would be great.

Thanks

Leon