The cpdf_set_font() function sets the current font face, font size and encoding. Currently only the standard postscript fonts are supported.
The last parameter encoding can take the following values: "MacRomanEncoding", "MacExpertEncoding", "WinAnsiEncoding", and "NULL". "NULL" stands for the font's built-in encoding.
See the ClibPDF Manual for more information, especially how to support asian fonts.