How is an icon attached to a PDF item in Exhibits?

Somewhere here it is advised to upload an icon or graphic with a PDF item. I would like to insert that icon/PDF combination in my exhibits. I haven't the slightest idea how to begin.

Inserting dual files as Exhibit items (with one being a graphic)displays only file names.

If you're trying to do that particular workaround, make sure that you're uploading the image file first.

I would've loved to find that Omeka extracts an icon automatically. How did you solved it travhard? A link maybe?