URL link in PDF accessed from pop-up not working

Hi I have set a pop-up on a clients site, with the post-submit message to include a clickable link to a PDF, which works fine. However there is a URL link in the PDF pack to the site (About page) and it doesn't work - "Safari can't open the specified address - first part of the address not valid". When I open the PDF on my laptop the link works fine, just not when opening the PDF from the post-submit message. Any ideas?

Thanks

Hi. Have you solved this yet?