How to find the link to an already existing PDF

I am creating a document with links to different online manuals.  Most of these manuals already have a link, I can just right click and find the link so I can add that to my document.  There is one manual where I right click and the link to the PDF doesnt show up.   How can i see the link of an already existing linked PDF? Ideally, i just want the reader to click from my document to the PDF document. Any help appreciated.