What is the (e.g., James Aldridge, John Man, or Jack Weatherford)? What format do you need (e.g., PDF, EPUB, FB2)? Is it a history book or a novel ?

(Smithsonian Institution). The Mongol Empire: Its Rise and Legacy by Michael Prawdin.

To find a "Mongol" book for free download, you have several options depending on whether you are looking for classic literature, modern fiction, or historical non-fiction.

For deeper historical research, hosts several out-of-print or open-access titles:

by Jeremiah Curtin: A historical account available for free via Project Gutenberg .

These texts are widely available for free because they are in the public domain or hosted by educational archives: