With recent advances in electronic design files, Computer Aided Design (CAD) has become a common place to store the design knowledge. Therefore, it is critical to secure the CAD files so that such valuable intellectual property is not available to competitors by internal users. Because most CAD drawings are composed of a collection of files with various extensions, there exist problems associated with the processing speed and the accuracy of CAD files encryption (decryption) using file based secure methods. In this study, an innovative idea of securing CAD files based on the workplace against illegal piracy of design knowledge is presented. The proposed technology is to store all design files in the secure workplace which can be accessed by the authorized users and design applications only using Application Programming Hooking at user level and System Service Table at kernel level. The technology is demonstrated in this paper using its implementation example in a civil engineering firm to verify it and CAD files can be shared among users without a concern of its leakage to the competitors by internal user.