Everything stays in this browser. No account, no upload, no telemetry. A
remote image in a document is linked, never fetched.
Your tabs are kept in this browser's storage, unencrypted. Anyone using this
browser profile can read them, and clearing site data deletes them.
Save (⌘S) writes a real file to disk. Do that for anything you want
to keep.
Opening a folder gives this page read access to everything under it, and
the browser remembers the folder until you close it. Files are read only
when you click one.