The operating system requirement for Acrobat DC is iOS 8 or newer.
The iOS 8 adoption rate is about 79% as of April 13, 2015.
App Store Distribution - Support - Apple Developer
Due to the iOS APIs used in Acrobat DC, it will not run on iOS 7 or older. It would require significant effort to make the app compatible with older iOS versions.
We apologize or the inconvenience if you are unable to update to iOS 8. You can continue using Adobe Reader for iOS (the previous version) on iOS 7.
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