If you do not have the latest version of Adobe Acrobat Reader installed, try installing it.
If you already have the latest version of Adobe Acrobat Reader, you may need to change your settings. To do this, logout of the OOPS application and close your browser window. Go to "Start", "Programs", "Adobe Acrobat Reader". Choose "Edit" from the menu bar in the top left of the page, then "Preferences". Depending upon what version of Acrobat Reader you are using, make sure the "Display PDF in browser" option is checked. Restart your browser and log into the OOPS application. Additional information is available on the Adobe Support website at:
https://helpx.adobe.com/support/reader.html