Create a certificate

I would design a page within Storyline that is your certificate. You can have people enter their name earlier in the course, or find some JavaScript that will pull their name from the LMS (I've attached a version of that created by Math Notermans, that worked for me). You can also find built-in variables that you can add so the current date appears on the certificate, etc. Then I would put a "print" button on the page. The JavaScript for printing any page in Storyline is just 

window.print();