Just a little report. I'm having problems with the pdf creator - it works fine in preview, but not once deployed as an html5 website.
Your demo (linked in your first post) is fine, but if I redeploy that, the pdf box remains blank, and the full screen isn't generated. Here's the link to my dropbox version. All I did was re-export your capx example.
For information, I'm using the current stable version of Construct 2 (release 158 64 bit) and I'm using Chrome.
I really like this idea - I'm producing educational games, and would love to generate an exportable certificate at the end of a quiz.