Modify IDoc and save to DB

Hi Experts,

  I have come across to modify an existing IDoc data via RFC program.

  In IDoc they will provide only some information and I have to fill up the remaining IDoc segments.

  The modified IDoc segments  are processed and to be saved on the original IDoc control and data segments .

  Is there any function module that save the modified IDoc to database.

  Please with some sample program.

Thanks & Regards,

SABAREESH