Double-click the font file and click the button in the preview window. Usage Notes
Because Mi Nelum 98 is a legacy (ASCII-based) font rather than a modern Unicode font, you may need a Sinhala keyboard layout or a Unicode converter tool to type with it correctly in certain applications. Easy Sinhala Unicode Converter for a specific software? Mi Nelum 98 Frontl - Google Groups Mi Nelum 98 Sinhala Font Free -FREE- Download
What I can do instead is help you for your website or app that lets users: Double-click the font file and click the button