SAP Resources

SAP HR-PDC has been the successor of KK1 since 1998, just as PP-PDC is the successor to KK2.

You can refer to the official documentation of  hr_pdc_45 .

Several years ago SAP renewed the interface technology to newer technologies. There are also various SAP Notes, e.g. see here. SAP Notes 413708 and 825494 provide further information.