The "Alcoholics Anonymous Big Book" is available in PDF format on the Alcoholics Anonymous website. Users can access the site and save copies of the PDF files that comprise the entire book.
The fourth edition of the "Big Book," which was published in 2001, is available in a series of PDF files on the AA website, with each chapter and appendix available as its own file. There are more than 20 individual files, which are available for free. It is not strictly necessary to download the files in order to read them, but those who wish to do so can easily save the files and print them at home.