Try this:
In Finder Go to: Macintosh HD/Library/Internet Plug-Ins and look for "AdobePDFViewerNPAPI.plugin" and move it to Disabled Plug-ins Folder (if you want to keep it). You will have to remove this file from the Internet Plug-Ins folder altogether.
In the ../Internet Plug-Ins folder you should also have the file called "AdobePDFViewer.plugin" leave this.
Relaunch Safari.