Notes about the HDML file extension:
To open this file type, a required software must be installed. Without it you only see a Windows message "The following file cannot be opened
" (Windows 7) or "How do you want to open this file?
" (Windows 10) if you double-click the file. There click on "More apps"
and choose a suitable software to view such files on your PC or from email attachments.
The HDML file type is primarily associated with 'Handheld Markup Language File'. In 1997, a company called Unwired Planet invented HDML and the browser that reads it, called the UP.Browser. At the time, it was the great hope of the so-called "third-generation," Web-enabled browser. But a lack of support on both ends left HDML temporarily high and dry. Recently, though, the WAP Forum, founded by Unwired Planet (since evolved into Phone.com and most recently Openwave) and such industry movers as Nokia and Motorola, unveiled WAP, the wireless application protocol, which in conjunction with this year's smaller, cheaper phones with greater screen real estate allows much more robust and widespread phone surfing.