It seems that the DHF is superior to the Design Dossier or Tech File in it’s thoroughness and documentation and that is why there seems to be a move in the EU toward the use of a DHF instead.
From the same link that pt58 posted: “Newer EU regulatory guidance documents are moving the TF/DD more in the direction of the DHF. However, a review of both descriptions above shows much commonality already, allowing the development of both files (DHF and TF/DD) almost concurrently, while supplementing the DHF with the DMR for a current TF/DD.”