| hcj | Hashcat Job Data |
| hck | MGS Hinge CK File |
| hcl | HotDocs Clause Archive |
| hcn | X90-OPUS Occupation Data |
| hcr | HydroCAD Rainfall Curve Data |
| hcs | eSubmission Builder Package |
| hcu | HydroCAD Units Definition |
| hcx | BinHex 2.0 Encoded Data |
| hcxs | Health Canada Form Data |
| hd2 | Poser Hand 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 | HansaWorld Database File |
| hdb | Maple Help Database |
| hdc | HD Tach Benchmark Data |
| hde | HRS Pro Encrypted Secure File |
| hdf | Hierarchical Data Format File |
| hdf4 | Hierarchical Data Format File |
| hdf5 | Hierarchical Data Format Release 5 |
| hdg | HDGraph Vectorial Graph Data |
| hdh | FM-ONE Host Side Bootcontrol Data |
| hdi | HotDocs Auto-Install File |
| hdk | HotDocs Registration File |
| hdkn | Hadouken BitTorrent Client Data |
| hdl | HotDocs Template Library |
| hdo | HelpDesk One Data |
| hdo | Snapform Designer Field Layer Data |
| hdp | FM-ONE Parameters Data |
| hdpart | hyperDENT Parts Data |
| hdpartz | hyperDENT Parts Archive |
| hdpmx | HotDocs Publisher Mapping XML |
| hdpp | hyperDENT Global Allowance Data |