The font that I want to use is not listed in Edit texts drop-down menu

Flash Decompiler Trillix uses fonts installed in your Windows OS, however only TrueType Outlines fonts are supported. PostScript Outlines fonts and bitmap fonts are not supported.

Please, make sure that the font that you would like to use is a TrueType Outlines font. In order to do so, go to Control Panel -> Fonts, select the font and double click on it to view its properties.