PDF stands for Portable Document Format; it is a file format which has captured the entire elements of a printed document as an electronic image which you can navigate, view, forward to someone else or print. PDF files are especially useful for documents like product vouchers, magazine articles, or flyers in which you want to conserve the unique graphic appearance online.
Sometimes it may undergo corruption or damage that ultimately leads the PDF file to become inaccessible. And reason could be anything like virus attack, improper system shut down, incompatible viewer program, improper download process, etc. Hence to regain access it should be recovered using good third party tool. One such tool I would recommend you is PDF file repair tool. Hope it will help you the way it helped me.....just visit the link below for further details