This is a followup to my original post found here. The only changes from the original are that this is now a Storyline 360 project and pdfmake has been updated to the latest version (v0.1.35 at time of posting).
The linked example provides a brief overview of how this works. I've tested this successfully in Internet Explorer, Chrome, Firefox, Chrome on Android and Safari on iOS.
The generated PDF certificate is very basic at the moment, you'll need to refer to the pdfmake documentation to update the design.
Feel free to have a look and re-use if it's useful.