HI,
Use functiona module FI_DOCUMENT_RECORD
with below parameters
I_AWTYP = 'PRCHG'
I_AWREF = mlhd-belnr
I_AWORG = mlhd-KJAHR
bukrs = MLIT-BUKRS
in the result table T_DOCUMENTS you will get all the documents realted to accounting and controling,
select one with AWTYP = 'BKPF' this is your accounting document
Regards
Ganesh