My son-in-law updated to the latest i0S 11.1 on his iPhone 6 -
some pdf files that were stored in iBooks disappeared and also from some of contacts.
Is there a way to recover missing data?
iPhone 6, iOS 10.2.1
First thing to do is a restart or forced restart on the iPhone and see if they reappear:
Restart your iPhone, iPad, or iPod touch - Apple Support
If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support (even though your screen is not black or frozen, see that section)
If those steps don't help the only remaining thing to try (that I know of) is to restore the device from a backup:
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
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Upgraded to the latest i0S and lost data. How do I recover that data?
