The Lima app can import all kind of files.
Due to iOS limitations, the "Open with Lima" feature can only be used from some apps, such as Apple Mail Mobile Safari iMovie or Readdle’s Documents 5 amongst others.
In the third-party app, start the file sharing (e.g. by long-pressing an email attachment in Apple Mail). An icon "Import with ∞ Lima" should be visible, allowing you to open the file with Lima.