Originally Posted by Faterson
By the way, Paul, I've just tried this on my Windows PC. I opened a Calibre folder in TotalCommander, picked up an EPUB file with the mouse and transferred it to the iTunes window, letting it drop there. It safely landed in the "Books" section.
So, I'm not sure our fellow poster's allegation is even true for iTunes. The EPUB file I dragged and dropped had never been "saved to disk" in Calibre. It's just an ordinary, converted EPUB file from a random Calibre folder.
Right, but only files from a single folder.
Using the app file transfer window you cannot add a directory structure, only files. As calibre stores each book in a separate directory, if you want to add your entire calibre library, you need to either visit each directory and add each book manually, or save to disk from calibre to put all the files in one directory, then you can add them all in one go. The latter is clearly the better option.
As you don't use iTunes, perhaps you should accept that people who do use it might have a better idea about what is required.