| h1c | Microsoft Help Collection Definition |
| h1d | Microsoft Help Validator File |
| h1h | Microsoft Help Merged Hierarchy File |
| h1k | Microsoft Help Keywords Index |
| h1q | Microsoft Help Merged Query Index |
| h1s | Microsoft Help Compiled Help Data |
| h1t | Microsoft Help Topic Definition |
| h1v | Microsoft Help VTopic Definition |
| h1w | Microsoft Help Merged Keyword Index |
| h2d | Hydrus-2D Data File |
| h2w | H2testw Data |
| h323 | H.323 IP Telephony Data |
| h3d | HyperView 3D Model |
| h4 | Hierarchical Data Format File |
| h5 | Hierarchical Data Format Release 5 |
| h77t | GEODAS MGD77T Header Data |
| h86 | CP/M Data |
| hal | HotDocs Answer Library |
| har | E-Sword Harmony Resource |
| harx | E-Sword v9.1 Harmony Resource |
| hash | EnCase Forensics Hash File |
| hb | Harwell Boeing Sparse Matrix |
| hbin | HITRAN Binary Output |
| hbk | Hex Workshop Bookmark File |
| hbn | Java Hibernate Data |
| hbp | HBPredicT Output |
| hbs | Line 6 POD HD Edit Set List |
| hbx | BinHex 2.0 Encoded Data |
| hc3 | AquaChem v3 Database |
| hcc | HydroCAD Prefab Chamber |
| hcd | ICM Hourly Climatic Database |
| hce | HydroCAD Hydrograph File |
| hcg | HCLab Document |
| hch | General CADD Hatch |
| hci | HydroCAD IDF Curve |
