Soak the paper in a bath of water for at least 30mins but it will withstand much longer. How long depends upon the paper and the temperature of the water. When soaked allow it to drip dry vertically (typically a printer will slap it on to a clean sheet of plastic for 5 mins) Then place it under some blotting paper and roller it until the surface of the paper is no longer shiny with water. A stack of paper will remain damp for hours between a couple of sheets of polythene.