How to read files outside the project's directory

Question

I'm new to flutter,I want to read some files outide the directory of my flutter project,let's say a file located in Desktop folder

here's how I tried

  Future<File> _getLocalFile() async {
      return File('/Users/xxx/Desktop/test.txt');
  }

then I got this error

[ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: FileSystemException: Cannot open file, path = '/Users/xxx/Desktop/test.txt' (OS Error: Operation not permitted, errno = 1)

Is there any way I can get the permission to deal with such files?