| hk | ASCA GIS Housekeeping Data |
| hkdb | iTunes Music Library |
| hkf | Microsoft .NET Install Hook File |
| hkh | HTML-Kit Help File |
| hkl | SHELX Reflection Data |
| hkm | Havok Movie File |
| hkp | Mentor Graphics HKP Database |
| hkt | Havok Tagfile |
| hkx | Havok XML Model File |
| hl | HeuristicLab Storage |
| hl7 | HL7 Standard Format Data |
| hlb | HP OpenVMS Help Library |
| hlc | ESO-MIDAS Help Command Data |
| hld | Structural Desktop Hold Data |
| hlg | BMERC Homolog Format Data |
| hli | Halcyon NSS License File |
| hlog | VMware ESXi Host Log |
| hlq | ESO-MIDAS Help Data |
| hlt | Hyperlynx Thermal Data |
| hlw | Hioki Logger Communicator Waveform Data |
| hlx | Hollex Cartridge Image |
| hlx | Multi-Edit Help Data |
| hl_ | Compressed HLP File |
| hmb | SPEEDTRONIC Mark IV HMI Bridge |
| hme | Smartphone Home Screen Theme |
| hmf | HOOPS Metafile |
| hmf | ANSYS Fluent Metafile |
| hmg | modhmm HMG model |
| hmm | HMMER Data |
| hmo | ROXIE Mesh Information |
| hmskin | Help and Manual Skin Data |
| hmt | HighMAT File |
| hnd | HNSKY Deep Sky Database |
| hnr | iGO Primo Defined Routes |
| hns | Hallo Northern Sky Data |
