Since the .atd to .dcf file conversion happens as a side-effect of a document type compilation, if you are upgrading to from a release prior to 4.3, you will not have your .atd files automatically converted for XML document types. You must manually convert the .atd files using the convert_atdfile command. Note that this command was removed in release 6.0, so you must use release 5.4 or earlier to convert an .atd file to a .dcf file.