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How do I transfer 4K video from the camera to my iPad?
Is your question the transfer then you want to buy a SD card adapter for your iPad.
Is the question howto open the file then the answer is that you have to convert AVCHD files to another iPad readable format or you have to create videos in MP4 , same applies more or less for XAVG-S file format.
You can use this thread as a possible starting point for your search.
Also according to the Imaging Edge Mobile compatibility page, your camera doesn't support sending 4K videos, so it can't be done wirelessly.