You can easily move a Case File from your iPad or Mac (maintaining the organizational structure of your documents, annotations, etc.) to another iPad or Mac. You can move the Case File to a USB thumb drive, or connected USB hard drive, or to the built-in Apple Files app. You can even AirDrop a Case File between devices.
Your Case File can be stored on Dropbox, or another cloud storage provider, but it must be zipped (compressed) before moving it from your local Files app to the cloud storage provider, and then unzipped (expanded) after it is moved back from the cloud storage provider to the local Files app on the other device.
You cannot open and work on a Case File while it is stored on Dropbox, or another cloud storage provider.