Exporting Hindi font from InDesign to PDF. I'm using World Ready but it's going wrong when exporting

Hi,   I have a book that mixes English and Hindi.  When it is laid up in Indesign, and shared via Share for Review, it is fine. But when exported to PDF, I get issues where the Hindi text changes and the spacing between the letters goes weird.   I am using World Ready composer, I have set the language to Hindi and I have tried with various standard Hindi fonts including Devanagari Sangam MN, ITF Devanagari and Arial Unicode MS  and I still get the same error. I am exporting to PDF at full resolution, but I get the same issue whether it is low, medium or maximum resolution.  Any advice much appreciated.