The ability to previewing imported items in the right windows of AC is as far as I know, ALWAYS a property setting in Adobe. I am using versions 8, 9, X and DC. Skipped 11. I know that 8 and 9 have no issues. For the other two, the two settings are the following.
For version X, go to Edit > Preferences > Internet and under Web Browser Options make sure that Display PDF in Browser is checked. This will allow the pdf to open in the right window pane of Imported Items if the Add-On is enabled. I wouldn't worry about the latter unless you are still having issues.
For the DC version, the only setting to worry about is the setting in Internet Explorer (at least that I can find). In I.E. under Tools > Manage Add-ons > All Add-ons > highlight PDF Reader and make sure it is enabled. This will allow viewing in AC. Disabling will make the PDF open in the Adobe reader.
I have never seen an issue where AC had anything to do with it.
