How to make single file from multiple PDF image?

Hi, it's my first question in SCN.

I promise my efforts for developing this site.

Lately, I made multiple PDF image by function 'CONVERT_OTFSPOOLJOB_2_PDF'.(each spool ID)

And I wanna make single .PDF file by merging these image in server directory(not local PC).

So I tried it following.

1. Each internal table resulted from CONVERT_OTFSPOOLJOB_2_PDF append one internal table.

   BL_PDF + MF_PDF → PDF

2. Excute following command.

  OPEN DATASET P_FILE FOR OUTPUT MESSAGE LV_MSG IN BINARY MODE.

  IF SY-SUBRC = 0.

    LOOP AT PDF.
      MOVE PDF TO FIELD.
      TRANSFER FIELD TO P_FILE.
      CLEAR PDF.
    ENDLOOP.

    CLOSE DATASET P_FILE.

  ENDIF.

But files was not merged, only last image was made as .PDF file instead.

How can I do it?

Thank you.