[MrLeap]

An epub is just a plain html webpage compressed into a zip and its extension changed from .zip to ".epub". Assuming you have a web browser, you have something that will almost certainly render your epubs contents.

PDF is not nearly as pleasant under the hood. It's down right lovecraftian.

[ablob]

The lovecraftian horror of pdf mostly comes into play through the sheer amount of software that supply almost correct pdf. It's not enough to be able to read pdf anymore, you also have to be able to deal with software that emits subtly wrong documents.

[PunchyHamster]

Adobe really have perfected act of making the most shoddy software that is still possible to sell

[m463]

I'm reminded of "PSD is not my favourite file format."

https://b3n.org/psd-is-not-my-favourite-file-format/

or in the code:

https://github.com/gco/xee/blob/master/XeePhotoshopLoader.m

[rcxdude]

That's part of it, but the design of PDF really doesn't help

[goodmythical]

I was floored to discover this recently when I clicked "edit" in calibre for the first time a few weeks ago.

Straight HTML, edit anything everywhere. Super slick.

[anenefan]

I'm aware thanks. Mostly it's just my preferred viewer is older than css4 but it's been nice to find out why that was the case.

PDFs can be painful as well, more often it's then using abode's pdf viewer, but it's far less common for me. There was a time many years ago when I understood PDF structures better, back when I chose to manually edit and fix a couple of malformed PDFs.