Why can't download powerpoint, pptx files in mail, to save to Keynote?

I have tried to send powerpoint presentations to my mail account to download and then save into Keynote. An error message comes up and says, "Can't download file"

I have worked with Apple tech support and at the Apple Store. they thought the pptx format woudn;'t work, so send in a variety formats, stipped out any macros, builds etc and nothing seems to change.

Rebooted the Ipad as well as reset the IPad and nothing seems to work.

Tech support can't figure out at the store or on line

Thanks