To answer your question of when do you need to generate a DHF vs. DHR is that the DHF is created during the first planning session of the developing the device. This includes every document from the inception of the device to the design transfer phase of the device. The DHF is more in depth of what document it contains, whereas the DHR contains a checklist that the device has been properly made, inspected, and passed its quality check. The DHR is used after design transfer and during the manufacturing phase of the device. Also, as you asked what are major differences in these documents, for one the DHF is not a document it is essentially an electronic container for all types of information from Risk Reviews, Meeting Minutes, Design Reviews, Design Change Processes, Design Specifications, etc. The DHR is a record maintained for each device or batch manufactured.