You would have to use iTunes.
AirDrop would be easier though.
[doublepost=1535841748][/doublepost]Or you could buy a lightning usb stick what Sandisk offer
Connect iPad to iTunes, Authorize as prompted on '10 iMac, select "TRUST" on iPad when prompted.
iTunes ... select icon at top-left-hand corner of iTunes for the iPad. Left side menu ... you'll see File Sharing.
Select, and therein you'll find Keynote and ability to sync that file to your Mac.