DDE (Dynamic Data Exchange) is an antiquated system for passing data between different programs on a Windows system. These days, it's not used much - although perhaps surprisingly, Explorer Replacement mode is actually implemented via DDE (for historical reasons more than anything).

Nonetheless, you may have an old program that supports a DDE interface, and should the need arise, it's possible to configure a button or hotkey to send what's called a DDE message to another application.

 

Above is an example command that establishes a DDE conversation and sends a command to another program. As this technique requires multiple command lines, you must create the command in the Advanced Command Editor. The four lines in the above function are: