You can now get all six volumes of the original Joseph Smith/B. H. Roberts History of the Church of Jesus Christ of Latter-Day Saints for Kindle, for free, on Project Gutenberg.
For academics the Joseph Smith Papers, which have superior editorial standards and more comprehensively cover their scope, have rightly gone a long way towards supplanting HotC. Any general reader ought to start with Saints vol. 1, which is just better–it covers the same time period, more readably, in fewer pages, to a higher standard of the historian’s craft. But HotC was the definitive Church history for generations, and now it’s at your fingerprints if you’d like to dive deeper. Have a look: Volume 1, Volume 2, Volume 3, Volume 4, Volume 5, Volume 6.
Thanks to all those who did the OCR proofreading/transcription for these volumes–I know that was a ton of work. (Anyone who looks carefully at the posting dates will see we got Vol. 1 released on PG in October 2014, and Vol. 6 was in November 2019. An embarrassing proportion of that gap relates to lag in my post-processing backlog, but there really was a whole bunch of proofreading done in there too.)