Files and images can be added to any form via a Hyperlink as part of the initial Description, Static Text, or to the Instructions for Fields.
First you will need to make your file into a hyperlink. Navigate to Settings> Pages, and click the Edit icon to edit a current page.
Select your file, and click Upload. Right click on the uploaded file link to copy the location/address. Paste the link in the URL area of the HTML code <a href="URL">any text here</a>. The words that you would like to appear as the link should go in the any text here part. Then copy your HTML code into your Form at Settings> Form> Form Name. You will need to click the Save Changes button to save your form.