Acrobat products have historically opened a PDF as long as the %PDF-header started anywhere within the first 1024 bytes of the file. No checks were performed on the extraneous bytes before the %PDF-header. However, the 10.1.5 and 11.0.01 updates improve security by enforcing stricter parsing of the PDF-header. The product now refuses to open the small fraction of PDFs that do not correctly start with the '%PDF-' header and an error appears:
Error: the document is damaged and cannot be repaired. Adobe Reader could not open because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded).
If you manage or administer software that automatically generates PDFs, modify the way the PDF is produced. Make sure that no extraneous bytes appear before %PDF at the head of the file.
If you are a customer or an enterprise IT professional, you can disable the header validation on machines by setting the appropriate preference. You can set this preference per user in HKCU or at the machine level for all users in HKLM. You can use a similar method on Mac OS by modifying the same plist preference. If the AVGeneral key does not exist, create it manually.
The HKLM path is generically:
For example, to change the behavior for Acrobat 11.0, create a DWORD at this location: HKLM\SOFTWARE\Adobe\Adobe Acrobat\11.0\AVGeneral\bValidateBytesBeforeHeader=dword:00000000
The HKCU path is generically:
For example, to change the behavior for Reader 10.0, create a DWORD at this location: HKCU\SOFTWARE\Adobe\Acrobat Reader\10.0\AVGeneral\bValidateBytesBeforeHeader=dword:00000000
Always change the product and version number in the preference path to match your installation. This method allows the PDF to display on machines you control.