The digital signature mechanism for the Adobe Acrobat PDF viewer only verifies the PE header of executable code for a plug-in, which can allow attackers to execute arbitrary code in certified mode by making the plug-in appear to be signed by Adobe.
Buffer overflow in Adobe Acrobat 4.05, Reader, Business Tools, and Fill In products that handle PDF files allows attackers to execute arbitrary commands via a long /Registry or /Ordering specifier.