| 11. | .hby | ROM image localisable resources |
| 12. | .hc | Header file |
| 13. | .hcm | Configuration file (IBM HCM) |
| 14. | .hcom | Sound (Macintosh) |
| 15. | .hcr | Production configuration file (IBM HCD/HCM) |
| 16. | .hda | Document file (HotDocs) |
| 17. | .hdf | Bitmap graphics Hierarchical Data Format (NCSA) ◊ Help file (Help Development Kit) |
| 18. | .hdl | Alternate download file listing (Procomm Plus) |
| 19. | .hdml | Handheld Device Markup Language |
| 20. | .hdr | Database header (Pc-File+) ◊ Datafile (Egret) ◊ Header information ◊ Message header (Procomm Plus - 1st Reader) |