Some very old Indian films (pre-1950s) may be in the public domain, but in India, copyright lasts for 60 years after the author's death. Few Bollywood films before 1960 are truly public domain. Check or National Film Archive of India .
In 2021, these global platforms expanded to India. They offer a rotating catalog of old Bollywood films. While you usually cannot "download" on the free tier, you can record or use their offline feature on mobile (for Plex Pass).