What is the best way to publish a book in the public domain?

Question

Books

Hello, a very, very good friend asked me how to put his book in the public domain. The problem is that it is very old, about 85 years old, and there are about 40 books on various topics in the collection. At the moment, he wants to lay out the first book, like the first pancake. I have never encountered this before and I would like to know what services are best done through so that you can comment on the entries and have a convenient download.
Thank you very much and have a great weekend!

Answer 1

LiveLib.ru
Flibusta
Librusek

Answer 2

Author's distribution on rutracker

Answer 3

Magazine "Samizdat"

Answer 4

another way - in the Caliber program, compose the library -> specify the path to the library to Caliber2OPDS and generate a static html directory from it -> put it on the network on narod.ru, in the GoogleDrive public folder, or, even easier - through dropbox, connecting it to what - either from a static content publishing service like pancake.io or cloudcannon.com - so that the generated directory placed there can be made available to everyone;