Foxit PDF Reader Configuration:
Install Foxit PDF Reader, check and ensure that "FoxitReaderBrowserAx.dll"(IE-based) and "npFoxitReaderPlugin.dll"(Firefox-based) are stored in the plugins folder in your Foxit Reader's main installation folder, somewhere like: 'C:\Program Files (x86)\Foxit Software\Foxit PDF Reader\plugins' or 'C:\Program Files\Foxit Software\Foxit PDF Reader\plugins'
Open PDF Reader, go to File > Preferences > File Association>Advanced, check "Include browser when setting default PDF viewer" and click Make Default PDF Viewer.
Restart Internet Explorer to activate your settings.
Note: Online PDF file could be opened within Internet Explorer without any configuration for Internet Explorer as long as you have Foxit PDF Reader Configuration done.