Protected Mode is based on Microsoft s Practical Windows Sandboxing technology. It is designed to restrict the vulnerability of an attacker who exploits Reader using a malicious PDF to gain full control of the underlying host system. The sandbox applies a set of more restrictive access control policies to these components, to limit what an attacker can do if an attacker successfully exploits Reader. The goal being to remove the most egregious vulnerabilities in a. reader is to remove or limit the ability of the. renderer to make these calls directly in the case that the. process is exploited.
Source: https://threatpost.com/assessing-adobe-reader-x-sandbox-112210/74695/