I stopped using Adobe Reader since few years and using Foxit reader as a PDF reader despite Foxit installs crappy toolbars without notifying readers (that seems to be fixed in latest version) happy with Foxit reader despite popular PDF reader from Adobe always in the news for vulnerabilities and for malware attacks and there is new security feature in Foxit reader which is safety reading mode.
Foxit introduced Trust Manager from version 3.3 (present is Foxit 3.3.1.0518) which allows users to allow or deny to run external commands in the PDF file to prevent attack from malicious content and viruses.
Enabling Safety reading Mode in Foxit Reader
From Foxit reader 3.3 safety reading mode is enabled by default.If unless some one manipulates its options
You can re-enable it by opening Foxit Reader Tools >Preferences select Trust Manager on the left pane and select Enable Safe Reading Mode on the right pane.
With Safe reading mode you can not open links, attachments from PDF file.However if you trust PDF file from trusted source you can disable it and able to open links and attachment and able to run other external commands folded in PDF file.
Simply uncheck before enable Safety reading mode under Preferences in Trust Manager to disable safe reading mode.It is recommended to keep safe reading mode enabled for protection.
Update: To get to Safety Reading Mode preference in Foxit Reader v6 onwards From Edit menu select Preferences>Trust Manager and uncheck Enable Safety Reading Mode.
To ease this process I recommend you to use Ctrl +K shortcut to open Preferences.