Which version should you choose? If you don't know what type your O/S is, the simplest way to figure it out is to try the 64-bit version. It runs 15%-30% faster than the 32-bit version. If it doesn't run, use the 32-bit version. If k2pdfopt is terminating abnormally (crashing) when you run it, try one of the "Older CPU" downloads below. They run approximately 20% slower than the optimized 32-bit d