Every now and then I get an e-mail in Outlook with an attachment that requires me to click to download the full message, after which the attachment doesn’t seem to be properly aware of it’s file type. Sometimes the attachment even says something like Invoice.pdf, but when you tap on it to open it you get a dialog asking you to CHOOSE AN APP.
Saving the file and trying to open via the File Explorer app doesn’t work either.
I discovered the solution by accident, as I tried to forward the e-mail to another e-mail address (GMail) with the hope that it could parse the attachment MIME type correctly.
Here’s the wierd bit, the draft created after you click on Forward shows the attachment with the correct file type. Tap on that attachment and it now opens in the default application (in this case the PDF opens in Edge which now previes PDF files).
All seems a bit crazy but it’s a very quick work around for a stupid bug.