The latest update has some sneaky nastiness added for some. When you are installing you need to make sure the tiny little box on the bottom left hand side of the screen (make ccleaner your default browser or some such) is not ticked. Please note it is quite small and has never been there before so I missed it. I thought I just needed to change the default browser back and all would be fine. Until I discovered all of my pdf files were now ccleaner files. Grrrrrr. The easiest solution is to just uninstall the browser. Personally I am planning to uninstall ccleaner too because I would never have thought they would pull such bad faith nonsense like this.