Domain driven design - Document conversion application

I have to create a document conversion application which has to be done using domain driven design.

Basically my application will receive data in xml\csv(as string input) format which is to be converted to a standard xml,json or csv format using xslt(as string output).

There are also some rules(stored in a relational database) which are applied to the data after converting to xml or json format.

The end interface might be Rest API or Wcf application.

But now I am confused as how I am supposed to create this using domain driven design.

What will be my domain models, will this include the rules which are stored in the database ?

and where I put the core format conversion logic, in the service layer or directly in API or wcf service classes ?

Thanks!