https://social.msdn.microsoft.com/Forums/vstudio/en-US/3713346d-95c7-4bf3-812c-0f8b2fa60d1c/dde-and-c?forum=csharpgeneral

You might wantto look at this thread - DDE in .net- where NDde CodePlex project is mentioned.
There are som helpful links:Dynamic Data Exchange Management Library
Dynamic Data Exchange (DDE) and NetDDE FAQ (see samples inside)