Spreadsheet attachment opens then won't in iPad Mail

A spreadsheet opened fine when I clicked on it in the email it came attached to. Then later when I wanted to view it again, it wouldn't open. It appeared as a blank page with only the document name and "Numbers Document" & the size. I don't have Numbers on my ipad; I have Excel. Why would it have opened the first time and then not open?

A related question: on a Mac, a copy of the attachment can be found in th Mail Downloads folder. Is there an equivalent place on an iPad (iOS 9) to find attached files?