How is it that I (or anyone) has not yet put links to this book in the Useful Material category?? I guess we keep thinking we’ve done so, and yet when I go to look for it (in order to pass it along) I can’t find it. 
Anyway, the best pdf scans are too large to archive here, and anything less than that can easily become illegible. So here are links to the three best pdf scans I can find at the Princeton Theological Archive. So far as I can tell each edition is identical in content, and visitors to the Archive can download versions of their choice for free.
A lighter scan of an 1831 printing, which reads a little easier than the darker scan, but it also has light water damage which could be a problem on some pages. At 26.4M it’s the largest download and has the fewest dl options. It has a scriptural index and the ‘missing’ material which was ported over to one of Winchester’s Lectures on Prophecies To Be Fulfilled.
A darker scan of an 1831 printing, which appears to have no damage but the contrast between the ink and the page may be a little more difficult to read. It has the scriptural index and the ‘missing’ fifth dialogue material. At 14.8M it’s the smallest download, but this could also reflect on its readability a little.
Possibly a 1902 reprint of a 1792 2nd edition. It’s missing the 5th dialogue material which was mostly ported to one of the Lectures (and the rest to the 4th dialogue), and it’s missing the scriptural index, but at 15.7M it looks pretty good.