As per Indian stamp act 1899, Stamping is a tax on the documents executed in India, share Certificates comes under the definition of Instrument, hence it is liable to be stamped as per the government specifications. Government gets huge revenues through the process of stamping.
Stamping provides the legality to the documents that are executed in India.
Rate of stamping differs from state to state.
Properly stamped documents are admissible as evidence in the court of law.