DDE stands for Dynamic Data Exchange, and it is a way for two programs to communicate with each other. http://msdn.microsoft.com/en-us/library/windows/desktop/ms648711(v=vs.85).aspx
Adobe Reader, or (Acrobat Standard/Pro) would be an example of a DDE server, in that when they are open they can accept unsolicited communication from client programs.
One client could be the fast launch utility.
Because the DDE server is local to your machine, only a server name needs to be decided upon. For instance prior to version 10 Adobe always used 'Acroview' as it's DDE Server Name. For some reason, Adobe claims 'security', They decided to change the DDE Server name for version 10 to AcroviewR10 for reader, and AcroviewA10 for Acrobat.
Because there was decades of old code which had never needed to change many programs stopped working, and began claiming that they couldn't connect to Acrobat.
Adobe, rightly, claimed that it was a bad practice to hard code the DDE Server name into your code, and that a better practice is to get the value from the Registry.
That would have been helpful but Adobe seems incapable of remembering to update this registry key when upgrading their software, even though they update the setting in their software.
For instance right now Adobe is setting the DDE Server name in the registry to AcroviewR10 for Reader 11. What is worse is that their software only responds to AcroviewR11.
So if you hardcode the server name, or create a function to determine what it should be, than you might be ok, but if you accept their good coding practices your applications will fail to work as expected, and your clients will think it is your fault.
Hope this helps.