1. First, visit the website of the National Digital Library, enter the keyword "National Digital Library"+"Name of host country" in the search engine, and find the corresponding link.
3. The search results page will list the books related to the query keywords, find the books you are interested in and click on the links of the books to view the detailed information.
4. If you have an e-book, you can download and read it directly. If you don't have an e-book, you can check the copyright information of the book, see if there are other publishers publishing the book, and try to buy a physical book.
It should be noted that not all the books in the National Digital Library have copyright-free versions, so it needs to be searched patiently. At the same time, when buying physical books, please be sure to choose formal channels to avoid buying pirated books.