When I double click on a Word attachment, Outlook tries to open it with “Windows Photo Viewer” which obviously fails.

Similarly, when I double click on a pdf-file, it tries to open it with Adobe Photoshop. Eventually, this will work for most pdf-files but loading Photoshop takes a while and only allows me to view a single page at once. As I want to read and not edit the pdf-file, I’d much rather open it with Adobe Reader instead.

How can I tell Outlook which program to open the attachment with?