I am developing an application,
i have coordinate pair in NAD27 to converted in NAD83 through .net c# program.I have reference at here
how to convert in objectarx ,If you can help me please comment..
Since you are using .NET, I assume you use AutoCAD/AutoCAD Map .NET API for your development. You are alomost there with the link you gave.
Since AutocAD Map 2010, you can do coordinate transformation in pure .NET API, called Map Platform API. In the same Autodesk online WikiHelp page you have found, instead of looking into ObjectARX Developer Guide or ObjectARX .NET Developer Guide, you look into Geospatial Platform Dev Guide. Go to "Coordinate System API" -> "Coordinate Transformation".