.NET interface to CHEMCAD is a DLL file. This DLL file is needed if you make a project on Visual Studio, MATLAB or other software which you want to connect with CHEMCAD. If you create a project using Visual Studio, it will make a copy of that DLL. If an update of the interface is released, user must change manually for each project. On the other hand, for MATLAB and other software, the location of the .NET interface DLL can be fixed so that user do not have to copy, paste and update each DLL file separately. To know more about .NET Interface visit .NET Interface.