What Default Fonts Are Included With iText?

It is probably referring to the PDF Standard 14 Fonts.

Actually you can find it out in the source code:

static BaseFont() {
        BuiltinFonts14.Add(COURIER, PdfName.COURIER);
        BuiltinFonts14.Add(COURIER_BOLD, PdfName.COURIER_BOLD);
        BuiltinFonts14.Add(COURIER_BOLDOBLIQUE, PdfName.COURIER_BOLDOBLIQUE);
        BuiltinFonts14.Add(COURIER_OBLIQUE, PdfName.COURIER_OBLIQUE);
        BuiltinFonts14.Add(HELVETICA, PdfName.HELVETICA);
        BuiltinFonts14.Add(HELVETICA_BOLD, PdfName.HELVETICA_BOLD);
        BuiltinFonts14.Add(HELVETICA_BOLDOBLIQUE, PdfName.HELVETICA_BOLDOBLIQUE);
        BuiltinFonts14.Add(HELVETICA_OBLIQUE, PdfName.HELVETICA_OBLIQUE);
        BuiltinFonts14.Add(SYMBOL, PdfName.SYMBOL);
        BuiltinFonts14.Add(TIMES_ROMAN, PdfName.TIMES_ROMAN);
        BuiltinFonts14.Add(TIMES_BOLD, PdfName.TIMES_BOLD);
        BuiltinFonts14.Add(TIMES_BOLDITALIC, PdfName.TIMES_BOLDITALIC);
        BuiltinFonts14.Add(TIMES_ITALIC, PdfName.TIMES_ITALIC);
        BuiltinFonts14.Add(ZAPFDINGBATS, PdfName.ZAPFDINGBATS);
    }