Download PDF instead of opening in browser

Dear WPDM development and support team,

First of all thank you very much for such a great plugin. ??

Unfortunately despite WPDM being an awesome plugin I have a problem I can’t sort out. All PDF files which are handled by WPDM are being opened in browser window instead of downloaded. Resumable Downloads, Output Buffering and Open in Browser options are disabled/unchecked. The strangest thing is it only happens when I left-click the download link. When I middle-click a prompt to download pops up.

What to do, how to live?? ??

Best regards, Dan.

The page I need help with: [log in to see the link]