Hello Saurabh,
You want to create standard Text which will have to be called with certainn code in PO with some custom development, instead try following
1) Create RFQ for Text with max.Qty and Max.Date for perticular vendor
2) Just enter this RFQ number in ME21N for creating PO it will defualt Text, so every time you need not enter text and just enter RFQ number
3) Make "Short Text"field display only, so that user will not be able to edit it
4)If short test needs to entered for certian other PO's, you can create a new document type for those
Please check if this works
Thanks
DD