I am having a similar problem. When I click on a PDF file that I created of one I received by email, Word opens and a file conversion box pops up. And PDFs received as attachments to emails do not have a "open with" choice when I right click on them. I have to save them to a file and then the "open with" option is available.
This is a new thing. I must have made some sort of change to some preference but I can't find an answer any where. Please help. I'm using Acrobat 8 on one PC and 6 on the other. It happens on both.
It sounds like Word has been associated with opening file with the .pdf extension.
My favorite quote - "Success is the ability to go from one failure to another with no loss of enthusiasm.