Some old text documents working with Arabic or Indic languages use 8-bit encoding, which required to use proprietary fonts. Such fonts can only use 256 glyphs, which is not sufficient for correct rendering of Devanagari (or other 10 Indic writing scripts).
If you only work with Latin-based languages (e.g. English, French, Polish, Czech or Turkish) then our OpenType Std fonts will meet your needs. If you also require support of Vietnamese, Russian or Greek, then you’ll need OpenType Pro fonts.