Running Win 7, 64 bit with Outlook 10 32 bit, when I upgrade Acrobat 8 to Acrobat XI, suddenly Outlook could no long be willing to run with the check mark under files>options>option 9 be able to open attached PDF's. It would choke up on start, shut down, uncheck that option and restart. Hence I would have to download attached PDF's onto the hard drive, and then open them.
One regedit help tip said to tell regedit with the dot command .regsvr32 "C:\Program Files\Adobe\Acrobat 11.0\PDFMaker\Office\PDFMOfficeAddin,dll" This apparently tells the registry that whenever you need PDFMOfficeAddin.dll this is where it actually is, no matter where you might have previously thought it would be. .
Regedit commands make me nervous, so I didn't run that, instead I did a hunt for where PDFMOfficeAddin.dll actually is.
I found it in C:\Program Files (x86)\Adobe\Acrobat\PDFMaker\Office\PDFMOfficeAddin,dll" , when it actually should have been in C"\Program Files\Adobe\Acrobat etc
I can only assume that in the upgrade from Acrobat 8 to XI, I answered some question wrong about my system and caused that. So rather than mess with the registry, I decided why don't I just put it (and the whole rest of the tree structure that follows to the right of Adobe) in C:\Program Files\Adobe etc and just leave that whole Acrobat file tree in BOTH PLACES.
Everything immediately got hunky-dory, running like a Swiss Watch.