I Am The Runner, The Pencils The Chaser. I Eat Up The Lead, I Choke On The Eraser

Riddle: I am the runner, The pencils the chaser. I eat up the lead, I choke on the eraser. When I am done, I become another one, To be used again. I am white And blank as well. I can be folded, Into a bell. My corners are cut perfectly, My lines are straight and blue. Me having black marks or not, Fully depends on you. What am I?