In brief, you can do this by applying a thick layer of spray adhesive to your *super clean* card/board in a well-ventilated area, away from any camera kit and computers, apply your print to it and smooth flat.
Leave for 24hours before sealing, using a mini paint roller and matt, water-based varnish if you wish to water-proof paper backdrops (vinyl backdrops won't need waterproofing).
Any over-hanging edges of paper can be cut off with a clean craft knife and if you want to get fancy you can soften the edges and corners of your MDF with fine-to-medium sandpaper.
We will update our step-by-step instructions and videos ASAP.
Made to order / on backorder - please see details below for lead times