My mother-in-law and my wife both noticed they can no longer open a PDF in Edge on their Alcatel IDOL 4S (each has one). I tried it on my Lumia 950XL and have the exact same issue. If we click a link in an email that is a link to a PDF, Edge launches and the screen flashes a few time then shows the message "This page is having a problem loading". The URL is pointing to the PDF file but does not open it. I have tried downloading Xodo but it can't open links, just stored PDF files. I wish they would just pull the plug instead of stringing us loyalists along like this, breaking more and more apps like water torture...drop, drip, drip...
That's a new bug with the new W10 Phone update. You'll need to use other PDF Viewers like Adobe Acrobat Reader, etc. until next update.