Save stored info

My dad has recently given me his old iPad mini. He used it for work and has quite a bit of important app/documents on it, which he has on his new iPad (through iCloud).

I absolutely can not lose any of this info for him.

This iPad has recently been backed up to iCloud, so is it safe to delete the documents/apps off of this device and will they still be available on his new device?

thank you!