Can document be stamped after being signed by the parties?

No, it cannot be stamped.  All the document need to de stamped and cancelled at the time of execution. Execution means the process of affixing the signature on the document. Adhesive stamps such as revenue stamps should also be cancelled by the party's signature across the face  of the stamp evidencing that the stamp were cancelled at the time of execution. Documents which are to be franked should not bear the date of execution and signature of the parties. The documents are to be dated at the time of franking and the parties have to execute the document after they are franked.