Stephane Charbonnier finished his manifesto just two days before he was killed in an attack on the offices of satirical magazine Charlie Hebdo in January 2015.
He was shot dead along with 11 others when gunmen stormed the building in Paris.
Charbonnier's book Open Letter: On Blasphemy, Islamophobia and the True Enemies of Free Expression is due to be published in the new year, but many have already received advance copies.
American chat show host and comedian Dave Rubin shared pictures of the front and back cover on Twitter.
And the words on just the front and back pages make for powerful reading alone:
If you think criticising religion is an expression of racism, if you think 'Islam' is the name of a people, if you think it's okay to make fun of everything except what is sacred to you, if you think sending blasphemers to jail will get you into heaven, if you think humour is incompatible with Islam
If you think a cartoon is more dangerous that an American drone, if you think Muslims have no sense of humour or irony...
... If you think the Zionists who run the world have paid a stooge to write this book, well, happy reading, because this letter is for you.