Hi,
Please use the following query to fetch purchase order lines attachment
SELECT
FDV.*
FROM
FND_ATTACHED_DOCUMENTS FAD,
FND_DOCUMENTS_VL FDV,
PO_LINES_ALL PLA,
PO_VERSIONS PV
WHERE
FAD.ENTITY_NAME = 'PO_LINES'
AND FAD.DOCUMENT_ID = FDV.DOCUMENT_ID
AND PLA.PO_LINE_ID = FAD.PK1_VALUE
AND FAD.CATEGORY_NAME           =                   'TO_SUPPLIER'
AND PK2_VALUE                                =                    PV.VERSION_ID
AND PLA.PO_HEADER_ID                =                    PV.PO_HEADER_ID
 AND NVL(PV.CO_NUM,0)                 =                    NVL(:PARAM_CO_NUM,
0)