Hello Vikram,
this issue usually happens when not an Adobe form is used but a SAPScript / SmartForm is converted to PDF.
Please check whether a converted SAPScript / SmartForm is used in this case.
If yes, and if you have a Unicode system, go to transaction SE38, run report RSTXPDF3, execute the option "List Settings", and enable parameter USE_CASCADING.
See SAP Note #1704919 - "Cascading PDF conversion for non-cascading device types" for details.
Also, this solution needs True Type fonts to be uploaded.
See (the attachment of) SAP Note #999712 - "PDF conversion for Unicode" for details.
Best regards,
Laszlo