Hi Sander,
Unfortunately the root cause of all date problems is that windows does not have a persian calendar!!! ( apparently recently added in win 10).
Anyway, this is the code used to the conversion. I am closing this thread.
DATA: greg_dt TYPE d.
DATA: dat_format TYPE xudatfm.
DATA: conv_hijra(10).
DATA: lv_date(10) TYPE c." -- Gregorain to Hijra calculation can be adjusted by maintaining values in TISLCAL as required.
GREG_DT = SOURCE_FIELDS-BILL_DATE .
TRY.
CALL METHOD cl_abap_datfm=>conv_date_int_to_ext
EXPORTING
im_datint = greg_dt
im_datfmdes = 'C'
IMPORTING ex_datext = conv_hijra.
CATCH cx_abap_datfm_format_unknown .
ENDTRY.
CONCATENATE conv_hijra+0(4) '/' conv_hijra+5(2) '/' conv_hijra+8(2) into lv_date .
RESULT = lv_date .