如果否则pdf文件存在codeigniter

<form method="post" action="<?php echo base_url('upload/process'); ?>" enctype="multipart/form-data">
    <input type="file" name="pdf_file" />
    <input type="submit" value="Upload" />
</form>

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Upload extends CI_Controller {

    public function __construct() {
        parent::__construct();
        $this->load->helper('url');
    }

    public function index() {
        $this->load->view('upload_form');
    }

    public function process() {
        $config['upload_path'] = './uploads/';
        $config['allowed_types'] = 'pdf';
        $config['max_size'] = 2048; // 2MB

        $this->load->library('upload', $config);

        if (!$this->upload->do_upload('pdf_file')) {
            $error = $this->upload->display_errors();
            // 处理上传错误
        } else {
            $data = $this->upload->data();
            $file_path = $data['full_path'];
            // 处理上传成功，可以对文件进行进一步操作，如存储到数据库或进行其他处理
        }
    }
}

$config['base_url'] = 'http://your-domain.com/';
$config['index_page'] = '';

$config['upload_path'] = './uploads/';
$config['allowed_types'] = 'pdf';
$config['max_size'] = 2048; // 2MB