Hello,
I know this problem was reported many months ago, but I am also experiencing this exact same issue, and have found no resolution to it yet. My user has a simple PDF embedded into an Excel 2010 document. Double click the PDF and it opens properly in Acrobat. If I close Acrobat, Excel freezes in the background (not responding). I have to force quit Excel to get back to Excel.
Also, if I double click on Acrobat again to re-open the application, it won't open. If I check Task Manager after Excel crashes, I can see that Acrobat.exe is still running in memory, and I have to force-quit it before I can re-open Acorbat.
Any progress on this issue?