Tap any font file with. Ttf or. Otf extension in your file explorer to preview it. You can also launch the Font Viewer directly and browse to open a font file. Font Viewer includes a slider to change font size and allow zooming on font details. Written and compiled on an Android phone thanks to RFO BASIC!, the GW library, and the BASIC! Compiler: RFO BASIC! GW lib. Basic!