I have version 10. When trying to download PDF docs from internet companies I alwasy get 'this version of Adobe Reader can't open document' What is the point of me being 'up to date' with Adobe if it doesn't work. ALSO I cannot uninstall this thing - it just won't go away.
Reader X can open all previous versions of all PDF files. The problem is probably with the files themselves. Maybe they got corrupted somehow.
Something worth trying is saving the files locally to your computer, and then opening them. If it still doesn't work, try contacting the company that provides them.