Configuration steps for enabling service object in ME21N

Hi Experts,

In one of my client there is a requirement of uploading documents ( like .pdf, .doc, .xls etc) in purchase order creation ( ME21N) . Present "Services for Object " option is not available in ME21N.

I have checked configuration steps for this facility in SPRO --> Cross- Application Components --> Document Management --> Control Data --> Maintain Screen for Object Link

Here Sap Object : EKPO and screen no : 248 was already assigned , and in Define Document types option also under KPR type EKPO & Screen no 248 already available.

But still I am not getting that "Services for Object" option  in ME21N.

Please let me know the step by step procedure for activating this option in ME21N.

Thanks in Advance.

Regards,

Aruna.