Ext. Type of file H C header HED HighEdit document HEIF High Efficiency Image file Format HGL HP Graphics language HLP Help text HMF HOOPS metafile HPJ Visual Basic help project HPP C++ program header HPL HP Graphics language HQX BinHex format HT HyperTerminal HTA Hypertext application HTM HTML document (Web page) HTML HTML document (Web page) HTX HTML extension HYC WordPerfect hyphen list