I can open the Sigil Epub using WinRAR and display all content. I can then open the OPF in my editor.
As an experiment, I have tried to change the cover image. I save the changed OPF and WinRAR asks if I wish to update the OPF. I click on "YES" and then WinRAR reports a corrupt file and makes no change to the OPF.
There must be something I'm missing or doing wrong. What's the secret?
