If you mean the disposable pee pads, you can only really use puppy pee pads if your bun isn't a chewer and will leave them alone, as ingesting pieces of the pads could potentially lead to a gastric blockage occurring.
I use puppy pads for my disabled rabbit, but the pads are primarily under fleece padding to absorb any urine so she doesn't usually have direct contact with them. But even when she did have direct contact she didn't chew them, so it hasn't been a problem for this particular rabbit. I have other rabbits that I could never use them with because they would chew and rip them up.
If your bun used to poop in the litter box and now isn't, you may want to examine why that might be happening, as it might be something you can correct. If it's just the round fecal poop outside the litter box and not urine, you don't really need to use puppy pads. I agree with strax that newspaper would be a better option(unless your bun wants to rip it up) or even a cut of fleece fabric, if you are really wanting something to line the cage with. Though personally I would just sweep up the poops, unless it's the sticky cecotropes that you are seeing and if so then you have a different problem on your hands as your rabbit should be ingesting those and you shouldn't even be really seeing them.
If you are still wanting to try the puppy pads, I just buy the bulk box of 100 pads at Costco as they are quite cheap this way and the pads are decent quality. Though if you are just wanting to try a few out, you may want to start with a small bag of them first, from somewhere like walmart.
