read data from a base64 encoded binary pdf file, format it and map it to JSON and save that as a UTF-8 text file

fn read_file(filename: &str) {
  let f = File::open(filename);
  ...
  let mut f = match f {
      Ok(file) => file,
      Err(e) => {
          println!("Error opening file: {:?}", e);
          return
      }
  };

  let mut contents = String::new();
  let result = f.read_to_string(&mut contents);
  match result {
      Ok(_) => {
          println!("File contents: {:?}", contents);
      }
      Err(e) => {
          println!("Error reading file: {:?}", e);
          return
      }
  }
}