A client application can use the DDE protocol to obtain a data item from a server (WM_DDE_REQUEST) or to submit a data item to a server (WM_DDE_POKE).

The client posts a WM_DDE_REQUEST message to the server, specifying an item and format by allocating a shared-memory object, filling in a DDESTRUCT data structure, and passing the data structure to WinDdePostMsg.

If the server is unable to satisfy the request, it sends the client a negative WM_DDE_ACK message. If the server can satisfy the request, it renders the item in the requested format, includes it with a DDESTRUCT data structure in a shared-memory object, and posts a WM_DDE_DATA message to the client.

Upon receiving a WM_DDE_DATA message, the client processes the data item. At the beginning of the shared-memory object, the DDESTRUCT data structure contains a status word indicating whether the sender requested an acknowledgment message. If the DDE_FACKREQ bit of the status word is set, the client must send the server a positive WM_DDE_ACK message.

Upon receiving a negative WM_DDE_ACK message, the client can ask for the same item again, specifying a different DDE format. Typically, a client first asks for the most complex format it can support, then steps down, if necessary, through progressively simpler formats, until it finds one the server can provide.