Currently Universal seems to preview only the first preview-able column in a table (the PDF in the screenshot below) and just shows this column twice. There is a second column (right under this pdf column) that holds an URL that should be previewed as well.
See question:
It would be great if Universal would know that it already previewed a preview-able column and then show the next preview-able column in a table. It might even be better to get more control over what is shown (for example via screentype-properties).