.otf
extension and TTF-OT (and SVG-OT) use the .ttf
extension, but they're both just OpenType fonts, only differing in the CFF/TFF(/CFF2/SVG) data blocks. As such, when we talk about otf
fonts we really mean 'Postscript opentype font' (which is a misnomer because CFF uses the Type2 language, not the PostScript language), and when we talk about ttf
fonts, we really mean 'TrueType opentype font'. However, an important thing to realise is that the extension does not in any way define the font; only its content does. We could rename the font to have a .gif
extension and it'd still be the kind of font the content specifies. So, for font engines, the extension doesn't matter in the slightest, in the same way that an image previewer will happily open a .jpg
file even if it has a .png
extension.otf
, which by convention is a 'postscript' font (but again, not really, it's Type2) into a ttf
, which by convention is a 'truetype' font, and thus cannot contain 'postscript' (but still, really Type2), with the added request that the ttf
should contain 'postscript outlines', doesn't make any sense: it's like asking how to convert a soft lead pencil into a hard lead pencil, but with soft lead: you're already done, you were asking how to create the thing you started with.otf
.