How am I able to save the photos / videos on my iPad that I have taken with my P4?

You have to import them to the iPad. The way I do it is I use a Lightning to SD card reader. I remove the SD card from the aircraft, plug it into an adapter and then place the adapter into the card reader. You then select the photos app on the Ipad and use the import function to import the photos or movies into the iPad.

I bought one of those lightning to camera sd card reader cables, only to find my iPad Air2 wouldn't play my 4K videos, in MOV or MP4 format.
Talk about cheesed off. Big Mozzarella... Ha


RedHotPoker

As well as above method, you can view and create basic edits using the 'Editor' function on the front page of DJI Go or DJI Go 4.
This will let you view the 'cached' images and video streamed over the Lightbridge from the aircraft. These of course are lower resolution than the originals on the SD card, but handy if you just want a quick snapshot or clip.
However what is interesting is that images can be transferred to your device from the aircraft SD card via the Lightbridge using the 'import' icon at the top left hand corner of the editor screen.
The caveat to this is that you cannot transfer 4k, 2.7k video nor DNG photos (would take too long to transfer large files) but you can transfer all other sizes (1080P etc and jpeg photos).
How the ipad handles the viewing would depend on the processing power and memory available. These methods work well on iPad pro 9.7.
These images /video could then be transferred to your computer via USB/Lightning cable using 'windows explorer' file manager if needed.