HTMLZ file - this is a zipped HTML eBook consisting of a single .html file and other supporting files. It can be read with Calibre software on a local computer - with index of search terms.
After purchase is completed, you will receive an email with the HTMLZ file attached. Be sure to check your spam/junk folders if the email doesn't appear in your inbox. Save the attachment (or click the Download link on the Document order details form) to your computer. Install Calibre on your computer (a free download from http://calibre-ebook.com) to view the book. Check with the reader manual for additional instructions.