place a sheet of light card (I used a whole A4 sheet ) on your ironing board then lay a piece of cling film smaller than that on top. Peel the top ply of your napkin away from the plain underside ( or sides if you have a 3 ply napkin) and discard the plain bits, cut down the image to the size you want for your final card topper ( I used a quarter of a napkin for an 8 inch card base), lay it face up on top of the cling film and cover with a sheet of cheap copy paper. Iron with a hot, steam free, iron for several seconds until the cling film seals the napkin to the card.
Remove the top paper to check everything has stuck, you can have another go if it hasn’t, then use scissors to cut the card flush with the napkin- take care, a trimmer will probably tear the napkin.
I had to fix brads in the corners as I couldn’t get a proper seal and when I used wink of Stella to embellish the reindeer, the napkin puffed off the cling film. Liquid pearls and stickles worked well though and my sentiment was peel offs stuck on card and foam tape mounted on the plainest bits of the napkin.
So at least one card in the stash for Christmas!