You can't. The main function of writing cats is to correct typos, not to lose weight. These two concepts are completely different. If you put your paper into the writing cat, the writing cat can quickly identify typos and then modify them according to the specific content. However, typo modification has nothing to do with weight reduction, so writing cats can't reduce the weight of paper. Therefore, it is not very helpful for the school exam. More depends on the paper itself.