Link.
Go to the "Help" menu in Safari and select "Installed Plug-ins". This will open a new tab displaying information about all of the currently installed plug-ins. Find the entry for Adobe Acrobat. Below it will be a line that reads something like:
Adobe® Acrobat® Plug-in for Web Browsers — from file “AdobePDFViewer.plugin”.
Note the name of the file from that line.
On your hard drive you will find a Library folder....