Writing guru Jane Friedman has made a useful chart describing the features of different ways to publication:
The PDF download is larger and easier to read with a magnifying glass feature.
One of the biggest changes I’ve noticed in the last six years is the attitude of big publishers towards eBooks. In 2013, those companies that issued a digital version of a print book, priced it the same or even more expensive, even though it cost them virtually nothing to store and distribute—unlike hard copies, which need warehouses, lorries and staff to handle. It almost felt like the Big 5 still secretly harboured a hatred of eBooks and were trying to kill them off by making them unaffordable.
More recently, several long-established publishers have opened imprints to promote digital sales, staffed by experienced and enthusiastic marketers. They often publish genre fiction by debut authors, which looks commercial but is still too risky to send to the printers. I think they’re still charging too much, which is why staying Indie is attractive to me, as I can ask as little as £1.99 on KDP Select to lure readers. Changing the price is as easy as a few mouse clicks. I can give my eBooks away for free for five days of every 90-day contract, to help promote sales. I haven’t heard of any mainstream digital publishers who’ll allow this.