This is a digital library—not a piracy site. The Internet Archive hosts millions of public domain films. Due to India’s copyright laws (life of author + 60 years), many pre-1960s Bollywood films or films whose copyright was not renewed fall into the public domain in the USA (though check Indian law).
The platforms above usually restrict downloads to "in-app only" (you cannot move the file to a USB drive). If you need a permanent digital copy of a 1970s classic for a personal collection (backup of a DVD you own), here is the legal approach: Free Bollywood Old Movies Download