That depends on the Apps you may be using.
While you can certainly connect an external drive, and access its files through the Files App, wether you can do so to from a specific App or are required to move the file into there app you are working with comes down to the App itself.
If the Apps you are interested in allow access to the Files App to browse the external drive, then you should be able to use the file directly from the external drive. Otherwise, you will need to move it into the App to work on it.
As powerful as it is, the new iPad Pros are still tablets by nature, and not full fledged computers.
See here for details: link-> Connect external devices or servers with Files on iPad - Apple Support