Using this font in your PDF templates, you will be able to render PDF invoices that contain beautiful Chinese characters, which would not be available with Helvetica font.
Usage:
Unzip the file. It contains 3 files. You must place all 3 files inside folder /components/com_invoices/helpers/dompdf/lib/fonts/
Then, in your invoice template, you just need to use the FireFly Sung font. A good way of doing so is by starting the template with a DIV forcing this font:
div style="font-family: FireFly Sung; font-size: 12px;"