| hcs | eSubmission Builder Package |
| hcss | Hyper Color Swatch Set |
| hct | Symantec LiveUpdate HCT Data |
| hcu | HydroCAD Units Definition |
| hcw | HTML Help Workshop Conversion Wizard Macro |
| hcx | BinHex 2.0 Encoded Data |
| hcx | Harvard ChartXL Chart Data |
| hcxs | Health Canada Form Data |
| hd2 | Poser Hand Data |
| 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 |
| hdb | Act! History Data |
| hdb | HansaWorld Database File |
| hdb | Maple Help Database |
| hdb | Watcher Database Data |
| hdc | Autodesk Land Desktop Hydrograph 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 |
