Download a PDF after user clicks 'Submit'

There's currently a form on our website that acts as a typical "contact us for more info" contact point; that is people fill out their name, email, phone number, etc. and we then get that as an email so we know to get in touch with them.

We're trying to change it slightly so that when a user checks a "Send me this" checkbox and hits 'Submit', it will automatically download a PDF tipsheet for them. So basically my situation is that I need to create a checkbox that will toggle the PDF download once 'Submit' is clicked. (Basically, the download will only start when someone requests it to.) The current Contact Us form resides here.

I'm not too familiar with form coding, so if anyone answers I might need some extra hand-holding.

m19