So, this is how I did this. I created an image content file with the cover page of the PDF. You have to copy the Content Key (located top middle of page) for adding to the thumbnail section of your document. Edit changes to the PDF document. Add this to the Link to Thumbnail section. /cms/delivery/media/(content key from the image) save the draft and publish it. In the CMS single item section in field mapping: add your info but in the image section select "link from thumbnail" it should show the image. Make sure you customize your link section to Heading and and your component field link should be source.  Hope that helps.