Digital Signature Certificates can be used in following ways:
1) For delivering and receiving digitally signed and encrypted mails.
2) In order to make safe digital transactions, or to figure out other participants of digital transactions.
3) Can be significant for eTendering, eProcurement, MCA [for Registrar of Companies efiling], Income Tax [for efiling income tax returns] Applications, and in various other applications.
4) In order to sign documents like MSWord, MSExcel, and PDFs.
5) Can be significant for establishing a paperless office.