| hlx | Multi-Edit Help Data |
| hlx | Hollex Cartridge Image |
| hl_ | Compressed HLP File |
| hm4 | Lorex Client Backup Data |
| hmb | SPEEDTRONIC Mark IV HMI Bridge |
| hmc | hyperCAD-S Model Data |
| hmc | HAMIC Data |
| hme | Smartphone Home Screen Theme |
| hmf | HOOPS Metafile |
| hmf | ANSYS Fluent Metafile |
| hmg | modhmm HMG model |
| hmgd | Microsoft Office Grammar Data |
| hmhd | Microsoft Word for Mac Hyphenation Data |
| hml | Thinkfree Office NEO XML Document |
| hmm | HMMER Data |
| hmmer | SAM HMMER-format Model |
| hmmr | SAM HMMER-format Model |
| hmo | ROXIE Mesh Information |
| hmp | HAHTsite Dynamic Server-side Image Map |
| hmr | Inertial Explorer Heading Data |
| hmrep | hyperMILL CAM Geometry Data |
| hms | WRAP HYD Message Data |
| hmskin | Help and Manual Skin Data |
| hmt | HighMAT File |
| hnd | HNSKY Deep Sky Database |
| hnf | HUMAX Receiver Settings Data |
| hnk | Internet Explorer HTML Help Index |
| hnr | iGO Primo Defined Routes |
| hns | Hallo Northern Sky Data |
| hnv | Hetero Number Viewer Input Data |
| ho | Knowledge Explorer Hierarchy Outline |
| hob | CARIS Hydrographic Object Binary Data |
| hobj | HALCON v12 Iconic Object |
| hobo | Onset HOBO Data Logger Data |
| hol | Microsoft Outlook Holiday Data |