Adobe Acrobat Pro DC Continuous Enhanced Security for standalone mode must be enabled.

Enhanced Security (ES) is a sandbox capability that restricts access to system resources. ES can be configured in two modes: Standalone mode is when Acrobat opens the desktop PDF client. ES Browser mode is when a PDF is opened via the browser plugin. When Enhanced Security is enabled and a PDF file tries to complete a restricted action from an untrusted location, a security warning must appear.Enhanced Security “hardens” the application against risky actions. It prevents cross domain access, prohibits script and data injection, blocks stream access to XObjects, silent printing, and execution of high privilege JavaScript.