Some attachments won’t open through Windows Live Mail

I'm running Windows Live Mail 2012 under Windows 10 Pro.  It's been working flawlessly for a long time, but all of a sudden I am unable to open some attachments simply by double-clicking the attachment icon in the incoming message.  Image files open Windows Photo Viewer and display, but .pdf, .doc and .xls, for example, just do nothing.  Hyperlinks within the message text open my browser just fine, however.  I can right-click the attachment icon and Save as... onto the Desktop, then open the attachment from there, but I can't drag it from the mail message to the Desktop anymore or use the right-click/Open option.  Thanks in advance for any tips on this.