I have to admit, I'm astonished by the ease with which one can be fooled into thinking they've procured the full and legitimate content of Darwin's signature work. A couple of easy clues, though:
Darwin refers in this version to a diagram in chapter IV, to illustrate "The Probable Effects of the Process of Natural Selection Through Divergence of Character and Extinction, On the Descendants of a Common Ancestor." This diagram is absent in this version, and this absence is what started me on the road to identifying this version as a fraud. I began to search for other editions of "Origins" to see if they included the diagram. And that search found not only that most versions did contain the diagram, but that the full text of this work ran to over 550 pages - twice as many as are included in this version.
I should also have known better than to have procured a free version. You truly do get what you pay for.
Be aware, as you look for a reliable version of the work, that there are many fraudulent versions out there. I won't go into detail on this, as this review concerns this specific version. But I can say that I've purchased a version that I am satisfied is a faithful rendering of the complete content. The ISBN number is 978-0-451-52906-0. It's the 150th anniversary edition, with an introduction by Julian Huxley. Still, don't take my word for it, and do your own due diligence. There is another "150th anniversary" version with an introduction by Ray Comfort, who is a Christian prothselitizer. So be careful.
Hopefully this will prevent you from having to start reading the work again from the beginning, as I've had to do. But I'm glad to have figured it out and separated fact from fiction.