| hcd | ICM Hourly Climatic Database |
| hce | HydroCAD Hydrograph File |
| hcg | HCLab Document |
| hch | General CADD Hatch |
| hci | HydroCAD IDF Curve |
| hck | MGS Hinge CK File |
| hcl | HotDocs Clause Archive |
| 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 |
| hdb | HansaWorld Database File |
| 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 |
| hdi | HotDocs Auto-Install File |
| hdk | HotDocs Registration File |
| hdl | HotDocs Template Library |
| hdpmx | HotDocs Publisher Mapping XML |
| hdr | DataFlex Database Header |
| hdr | Mail.dat Header File |
| hdr | Microsoft IIS NNTP Header Data |
| hdumx | HotDocs User Mapping XML |
| hdz | Poser Compressed Hand Data |
| he2 | Hierarchical Data Format File |
| he5 | Hierarchical Data Format Release 5 |
| hea | PhysioBank Header File |
| hef | HEAT Export Data |
| heg | GRABLOX HEG Data |
