Cronos75,
I'll offer a few thoughts since no one else has. I'm not sure, though, that I'll be very helpful.
I think the biggest challenge here is the invocation of a structuring mechanism, not general document management. It is normally very simple to open a new document with the Open() method, once you figure out how the input parameter scheme works. The addition of the DITA structure, though, is a different story. Presumably, you would need to invoke the Structure Generator using a conversion table which is possible, but this process could have much risk for error. You would probably have to paste the text into a separate file, structure it, then copy it into the existing DITA structure in the target file. Lots of things could go wrong there.
Anyway, I'm sure what you want to do is possible with ES, but you'll have lots of work to do.
Russ