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.
Navigate to Settings> Forms and click on the form you would like to edit.
Attaching a File
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.
Click the Pencil icon to edit the page, and then upload your file via the Insert File button.
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.