Due to the prominent improvements in the present software engineering, conversion from one programming language to another programming language becomes important task of the industry. Industrial survey shows that major components of development cost of all software goes to maintaining and updating the system software or application package for meeting the current scenario and / or user's satisfaction. In this paper, proposed a Software Development tool (SDT) called `Legacy Code Conversion Kit (LCCK)' for conversion of one object oriented programming language (Source Language) to another object oriented programming language (Destination Language). Design Rationale to Source Graph (DR-SG) is our proposed model that formed a graph from Design Pattern documentation and linked to a source code base. The DR-SG allows developers to trace design concepts through design documentation. This proposed work, completely and confidently satisfying high-level design goals when performing software change tasks. The result of our implementation, from C++ to Java conversion is shown in the chapters.