A will is a legal document which explicitly states how the person wishes to divide their property after death. If the deceased has died intestate (without writing a will), leaving behind debt and securities, then a document called succession certificate is needed for collecting debts and securities due to her/him.
This certificate also indemnifies the debtors regarding all the payments made or the dealings done in good faith, from the holder of the certificate. This is precisely the reason many people concerned with these types of dealings ask for a succession certificate before beginning the proceedings for settling debts of the deceased with the claimant.
A succession certificate is valid throughout India.