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If your device isn’t eligible for iOS 13, it’s not possible to update it to that version. Also, Apple doesn’t sign iOS 13 for any Apple device. If you try installing that software version on your device, you’ll get an error warning, such as “The device isn't eligible for the requested build.", or “There was a problem downloading the software.", and you won’t be able to proceed.
Additionally, your iPad might not be able to handle iOS 13 because of its hardware.