Tap the attachment icon to download it to your device, and you’ll see the icon turn into an iBooks one. Tap and hold on the file and an “Open in iBooks” will pop up. Tap that, and your iPad or iPhone will open iBooks and then open the epub file you just sent.Does iPad read EPUB file format?
Directly on the iPAD (recommended) Make sure the free iBooks app is on your iPad. Follow the link from Safari to reach the ePub document. Select "Open in iBooks" on the iPad. The eBook will open and be added to your iBooks collection. From now on, you can open the ePub document from the iBooks app on your iPad.