| hd3 | Huidu LED Matrix Data |
| hda | HotDocs Auto-Assemble File |
| hda | Houdini Digital Asset Library |
| hdalc | Houdini Indie Digital Asset Library |
| hdanc | Houdini Non-commercial Digital Asset Library |
| hdat | Objective Analysis HDAT Data |
| hdat | vStaticIP Internal Data |
| hdb | Act! History Data |
| hdb | HansaWorld Database File |
| hdb | Maple Help Database |
| hdb | Watcher Database Data |
| hdc | HD Tach Benchmark Data |
| hdc | HelloDOC Medical Data |
| hdd | HelloDOC Medical Database |
| hde | HRS Pro Encrypted Secure File |
| hdf | HEC-RAS Data |
| hdf | Hierarchical Data Format File |
| hdf | Home Inspector Pro Inspection Document |
| hdf4 | Hierarchical Data Format File |
| hdf5 | Hierarchical Data Format Release 5 |
| hdg | HDGraph Vectorial Graph Data |
| hdh | FM-ONE Host Side Bootcontrol Data |
| hdi | HelloDOC Medical Database Index |
| hdi | HotDocs Auto-Install File |
| hdk | HotDocs Registration File |
| hdkn | Hadouken BitTorrent Client Data |
| hdl | HotDocs Template Library |
| hdl | Procomm Plus Alternate Download File List |
| hdo | HelpDesk One Data |
| hdo | Snapform Designer Field Layer Data |
