Downloadable Products

In my store I sell rings.
Problem with rings is that customers don't know their finger size, so I created a file that customers can print and check their finger sizes.

How do I let my visitors download a 'product'?
I need them to click on something and then they'll get to a page with the file I created ready to be downloaded (Printable)

my site: http://noajewelry.com
A page with rings: http://noajewelry.com/Rings%20-%20preci ... 0gemstones

I use Open cart Version 1.5.1

Thank you!

If you insert it as a download , the customer would only be able to download it after an order. I think would be better to upload it somewhere on your server and link to it on the product page.

Thank you