You likely do not need malpractice insurance to perform document review. Most document review projects do not require malpractice insurance as they only involve a first pass at the documents. These documents usually receive a second pass by lawyers in the firm or company hosting the review. The risk is borne by these lawyers as they are ultimately responsible for producing the documents to the opposing parties. If your project goes beyond a first pass or you just want to be sure, you may check with your project host as well as your bar association to confirm whether you need malpractice insurance.