Adding a Download field to a form

Adding a Download field to a form

I want to set up a form on my website so that people can download a pdf file once they have submitted their email details. It has been really easy to set up the template but I cannot locate a field with the function. I can see file upload, but not download. This is the main task I want to add to my website as part of the "sales funnel" so hope there is the option.