Your Case File can be archived and stored on Dropbox, or another cloud storage provider, but it needs to be zipped (compressed) before moving it from your local storage to the cloud storage provider; and then unzipped (expanded) after it is moved back from the cloud storage provider to local storage.
You cannot open and work on a Case File while it is stored on Dropbox, or another cloud storage provider.
The reason for this is that Dropbox and other third party cloud storage providers do not support the Apple package file format on iPadOS. While package files appear to be a single file when viewed on Apple platforms, they actually contain many other files and are represented as a folder on non-Mac computers and most web browsers. Storing, or even temporarily transferring an uncompressed Case File to an unsupported location, may result in a corrupted Case File that can no longer be opened.