There are some iOS apps appear in the file sharing list of my iPad that does not appear in my iPhone file sharing list. Why is that and why iBook App does not show on the sharing list of my iPad?
iPad
The apps which show on the file sharing section on your iPad when connected to your computer's iTunes, you have exactly the same apps installed on your iPhone - they are not separate iPad and iPhone apps that you have installed on your iPad/iPhone, and only the iPad version supports file sharing ?
For iBooks, that won't show, it doesn't support file sharing. You can add ibooks / epubs / PDFs to your computer's iTunes library (the iBooks app if you are using a Mac with OS X Mavericks on it) via File > Add To Library, and you sync them to a device via its Books tab :
If you want to copy them off the device to your computer's iTunes (to the iBooks app on Mavericks) then File > Devices > Transfer Purchases will copy them over (that will copy PDFs and epubs from the iBooks app on your device, not just ibooks).
I see some iOS apps in the file sharing list for my iPad device but I do not see the same APP on the file sharing list of my other iOS device
