Recover Corrupt PDF Files
If you have a corrupt PDF file that you can't open, particularly one which gives you an error message like this:
. . . about a root object missing, you should be able to recover the PDF with PDF Recovery from Sysinfo Tools. See: http://www.sysinfotools.com/recovery/pdf-recovery.php . I have used it successfully to open a PDF file which gave me this same error message. The trial version will only recover every other page, but a license only costs $59.