want to read the contents of files and need validation

In my CodeIgniter project, I want to read the contents of files and need validation to confirm if a file is selected. I have written code in the controller using $this->form_validation->set_rules() function, but I am getting an error that says "The Project Estimation File field is required" even after selecting a file. What could be the issue?

See: https://codeigniter.com/user_guide/libra...le-uploads