For a few years, Google Book Search has provided PDF downloads of public domain books. The books came with a page listing some guidelines that Google asked people to follow and the same guidelines are listed in their Google Book Search help center. …
[The guidelines have been changed] – it used to say that only non-commercial use is [allowed]. Now it has been replaced by two new guidelines: no hosting, and no reprints including helping people reprint.
Google: Don’t re-host public domain books from Google Books 2 February 2009
Yakov Shafranovich, Change in Google Book Search Guidelines for Public Domain Books, Personal Website of Yakov Shafranovich, January 30, 2009.