I've made rubber stamps from my kitties' paw prints. What I'd suggest is using a darker craft ink. The water-based ink just doesn't show up with a paw print impression, and since you can't tell them to "press down" the image shows up much lighter.
First, I wet a warm washcloth with baby wash. Then I set up my paper and opened the ink pad. I used SU's craft ink. IME a back paw's impression works better than the front. Get a few images if you can, then immediately wash the paw pad thoroughly and wipe dry.
I'd suggest doing this after a long play session. . . so kitty is tired.
PM me for details if you like.
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Happiness is being kneaded.
Avatar is my childhood kitty, Berries.