This widely accepted ebook format is supported by many reading devices and apps. It's the standard format for the International Digital Publishing Forum (IDPF). Apple Books uses ePub, and many other platforms support it. It's a flexible format that can be generated as reflowable or fixed-layout, depending on the type of content. (See here for more on Fixed layout vs Reflowable.
As of May 2023, the ePub standard is ePub3.3, described here
These formats are used by Amazon for its Kindle devices and apps. MOBI is the older format, while KF8 (Kindle Format 8) and AZW3 are newer and support more advanced features. If you're distributing directly to Amazon, they'll often convert ePub files to their proprietary formats. When you use Amazon's Kindle Direct Publishing (KDP) platform, you can upload an ePub file, and they will automatically convert it.
While technically an ebook format, PDFs are not reflowable like ePub or MOBI, which means they maintain a fixed layout regardless of the device or screen size. They're great for content where layout is essential (like graphic novels or magazines), but they might not offer a great reading experience on smaller devices.
Given the above formats, here's a strategy for publishers:For Maximum Flexibility and Compatibility,
start with an ePub file. It's versatile, widely accepted, and can be converted to other formats relatively easily.For Amazon
If you're publishing on Amazon, they will take your ePub and convert it. However, if you want more control over the final appearance on Kindle devices, you might consider converting the ePub to KF8/AZW3 yourself using Amazon's tools like Kindle Previewer and KindleGen.For Apple
Apple Books primarily uses ePub, so you're good to go with that format.
ePub3 is the most versatile and widely accepted format for ebook distribution. Start with a high-quality ePub file, and then consider additional formats based on specific platform requirements or needs.