That is because the new PDF files made with the latest version of Adobe Acrobat can not be read by Preview, Mac’s program that is associated with PDF files. So, I suggest you download and install the latest version of Adobe Acrobat here:
Download Acrobat Reader for Mac
And if already have Acrobat Reader on your Mac and you still can’t read a PDF, then download the latest version of Adobe Acrobat. As of this writing, the latest version is 8.1.1 for Mac.
Same goes for you PC users, by the way. Can’t read a PDF? Download the latest version of Acrobat Reader.
