I have similar. All my PDF files now show as HTML in Explorer and if I click to open they "download" to make a duplicate copy also in HTML
I confirmed by creating a PDF file onto my desktop but it shows as HTML and not a PDF.
I am running Win 7 and installed the Reader update to 11.0.09 earlier today.
Have confirmed that Acrobat 9.5 will open the HTML files as PDF files so this seems to confirm the bug is not in the files but in reader 11
