The following free textbooks for middle- and high-school learners are available as pdf files that can be downloaded or added to your Google drive. In addition, at the end of this post are a couple of elementary world history readers and additional resources.
Journey Across Time Printable Worksheets: with blank outlines, reading check questions and vocabulary for each chapter.
For both ancient civilization textbooks, at the site, click on individual chapters under the book's cover. Click on the cover and you're taken to the companion website. Continue scrolling down the page, and you can download a variety of world history readers such as these:
High School Textbooks:
Scroll down the page for book chapters, Powerpoints and worksheets.
Download paper dolls to explore world history and fashion through the ages. At the site, there's clothing for Romeo and Juliet (1500s), Jane Austen t(1800s), the Edwardian Age (1900s) and others. There's also clothing to make dolls for Ancient Egypt and Rome, the Vikings, Asia, and North American Indians. It's all free.