By the way, to paint jack o lantern stencils on a craft pumpkin is the same as painting a real pumpkin. Find out how at Halloween Pumpkin Stencils. It’s real easy and lot's of fun.
However, carving a craft pumpkin is a little different from carving a real pumpkin. You’ll need to cut out the stencil islands and trace it onto the pumpkin instead of using a punch tool. The punch tool is not very effective in penetrating the plastic. Trim the excess paper from around the outside of the stencil with scissors making sure to leave at least a ½ inch border on all sides for the tape. Line up the pattern on the pumpkin and tape both sides of the stencil, top and bottom. To tape the corners, you may need to crease the stencil. Depending on the roundness of the pumpkin, this may distort your design so try to make the creases where the pattern will be the least distorted. Trace the stencil onto the pumpkin surface and remove.
Use a sharp, triangular blade X-Acto or craft knife instead of a carving saw. A smooth up and down saw motion is best to keep control of the blade. Only use gentle pressure to avoid stressing and breaking the tool or the pumpkin. It’s best to start in the center of the design and work your way out. You may need to rotate the pumpkin in your lap to keep the side that you are cutting closer to your hand. To cut sharp corners, remove the saw blade and re-insert it at the new angle. Use your finger to push the cut pieces out from the inside of the pumpkin. Cut large areas into smaller ones for easier removal.
Also, the plastic pumpkins are flammable so you need to use a battery operated tea light candle inside or install a night light kit. Instead of cutting a lid on top, cut a circle in the bottom to sit the pumpkin over the light source.