It's not really about what the Numbers guy does but probably what FileDocument lets it do it. I have never used FileDocument with an iOS app. I do have a macOS application with FileDocument. If I open and then close a document and then move it under a different volume or a folder, the application is still able to open it. But it won't if I move a file to the dumpster.
Topic:
App & System Services
SubTopic:
General
Tags: