Okay, but according to the screenshot that you provided, you are doing this after you opened the file, then hit share, then More. Try opening the mail message, then instead of opening the document by just tapping on it, press and hold for the attachment to open. That should open it in a smaller screen, then you should see Quick Look, Share, and Copy in the lower left corner. Tap share there, then once the second screen comes up swipe to the left until you see More again, and tap on it there. That seems to bring up a set of app suggestions. I was able to duplicate the error you reported that hitting More the other way closed the mail message. It could be a bug, but I would go to Feedback - iPhone - Apple and report that to Apple.