Chess books are a great way to improve at chess. However, they can be expensive and you may not want to buy a book you don't know much about. Fortunately, there is Archive.org that has many chess books all for free. However, simply looking up chess is not good enough. By using this link at the bottom, you will have access to 87 Chess books. Scroll down to pdf and you will have access to all of them.
archive.org/details/CHESSGrandmaster/101%20Chess%20Openings%20Surprises%20-%20by%20Graham%20Burgess/page/n7/mode/2up
archive.org/details/CHESSGrandmaster/101%20Chess%20Openings%20Surprises%20-%20by%20Graham%20Burgess/page/n7/mode/2up