Have Safari open PDFs using Preview instead of Acrobat

If you have installed Adobe Acrobat or another program, it may have installed a plugin into your (Main Drive)/Library/Internet Plug-Ins . In my case, after Adobe Acrobat had installed an AdobePDFViewer plug-in in the above directory. Delete or move the plugin from that folder and Mac OS X will once again open PDFs in Safari using Apple’s Preview instead.

Reference : http://kb.adobe.com/selfservice/viewContent.do?externalId=333545&sliceId=2