... course you can. Most of iBooks support ePub.For this [iPubsoft ...
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I am afraid that iBook files can be read only on an iOS device. The future is uncertain regarding their usability on Windows PCs.
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In iTunes, click on your device and "Transfer purchases". It copies the books to your local hard disk. The rest depends on OS you use.
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iBooks do not allow us to read them on pc, because they are protected and pc can not relieve the limitation by itself. But there is a method how to do that. Surf the web.
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