Alt+Double Left Click the .pdf file and click change which application to open with. Locate the new adobe reader from the browse option, target directory of course being c:\program files\adobe and select the option, apply the settings.
Adobe also has an web viewer option and background downloader which can be access via adobe reader under;
Edit > Preferences > Internet on the left navigation, set your options here.
If however this does not fix the issue, then there is a conflict with the adobe products, all adobe products have to be removed because of a corrupt issue in the registry, once all adobe application have been removed (reader applications only) you need to clean the registry (crap cleaner - piriform) then restart the machine after crap cleaner is complete, once restarted reinstall your adobe reader that you want to use.
Only reason im suggesting this, is we just had a client having the same problem with adobe reader 9 and acrobat reader 9. Almost the same but one allows for editing and creating pdf's.