Adobe has a plethora of attachments and add-ons that often create tpye specific file identities that bear only a passing resemblance to a PDF file, one of the quirks of Adobe's longevity I suppose, one possible thing you could try would be to 'COPY' the files to either a seprate folder or disk and alter the files too read as PDF then try agian from that location, withouth knowing what your vendor actualy used to create the files other than the base program even the huge database of adobe is going to be hard pressed to provide a suitable solution.
It is possible to alter the default behavoir of Adobe reader in the way it handles file extentions though this does require a working knowledge of the registry. some details can be found here:
http://www.adobe.com/cfusion/knowled....cfm?id=331371