Hi Jan,
Thank you for your purchase.

Unfortunately something like this is not possible with the plugin build in features but I can give you some workaround.
 
First in you will need to set Column type for that column to be Image and Editor input type to be One-line edit.

Then in field value you must enter the data in this format

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQdC9d6Z2Al0vMxQRqFc0230CUo-C-1BhIC3I5R9XTFw7MQLdeP||https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQdC9d6Z2Al0vMxQRqFc0230CUo-C-1BhIC3I5R9XTFw7MQLdeP

Or the shorter code would look like this 

http://domain.com/thumb.png||http://domain.com/fullsize.png

(You can change the URL to your desire and put the URL from that PDF)

You will notice the "two sticks" | | sign

If the content of the cells contains a combination of “two sticks” – || – then everything to the left of this combination is used as a link to the thumbnail, and everything to the right as a link to the full image size.


Hope this can help you out.

Best regards.