The .bnk file is designed to work with Examview, which can be obtained free from einstruction.com. The software allows you to change all the problems with a single command, so that a teacher can have multiple versions of a test. The numbers in each problem will change. In some cases, I've designed it so that the entire problem will change. Also, the answer order will change. A Word version or pdf version would be stuck in a single static version of a problem. With the dynamic feature of Examview, you can create thousands of versions of a test.