Hi,
Purchasing document in CJI3 is coming as standard. No any enhancement needed.
1)CJI3
Execute CJI3->choose standard layout 2SAP->execute.
Now in next screen>Change layout icon-> drag purchasing document to left side from right side->continue
Now Purchasing Document will appear in CJI3
2)CJI5
In CJI5, Purchasing document will refer as Ref Document Number
Select->drag->continue
After that PR/PO will be shown in CJI5
Regards
Shishir