I have a user who has the latest version of Adobe Acrobat and Reader installed on his PC running Windows 7 Pro SP1 which is up to date on patches.
He was unable to open any pdf documents attached to email and was getting an error from Acrobat saying it couldn't open them. I changed the default file association for .pdf file from Acrobat to Reader and now he can open most pdf attachments. The only ones he is having a problem with are ones that come from his bank in what he was told by his banker are secure emails.
What happens when he clicks on the pdf attachment in the emails from his bank is that he gets a popup with Adobe Acrobat in the title bar of the popup and the message that says "Cannot use Adobe Reader to view PDF in your web browser. Reader will now exit. Please exit your browser and try again." The buttons to click on are OK and Cancel. If he clicks OK, the popup goes away and the pdf then opens in Reader.
So while he can view the pdf, he gets the annoying popup that he has to click through. Is there any way to get rid of that error message popup so when he clicks on the pdf in the secure emails, that it just opens without error like the pdf's do from non-secure emails?