Free Patent Databases

Indian Patent Office Database search website
https://ipindiaservices.gov.in/publicsearch
Patentscope Database

The Patentscope database of World Intellectual Property Organization provides access to international Patent Cooperation Treaty (PCT) applications in full text format on the day of publication.

https://www.wipo.int/patentscope/en/
European Patent Office
http://ep.espacenet.com/
US Patent and Trademark Office
http://patft.uspto.gov/