PHP7でPDFファイルをダウンロードする際のエラーの対処方法

$pdfFilePath = 'pdf/test.pdf';

if (file_exists($pdfFilePath)) {
    // 下载PDF文件的代码
} else {
    echo "文件不存在或路径错误！";
}

header('Content-Type: application/pdf');
header('Content-Disposition: attachment; filename="test.pdf"');

$pdfFilePath = 'pdf/test.pdf';

if (file_exists($pdfFilePath)) {
    header('Content-Type: application/pdf');
    header('Content-Disposition: attachment; filename="test.pdf"');
    readfile($pdfFilePath);
} else {
    echo "文件不存在或路径错误！";
}

$pdfFilePath = 'pdf/big_file.pdf';

if (file_exists($pdfFilePath)) {
    header('Content-Type: application/pdf');
    header('Content-Disposition: attachment; filename="big_file.pdf"');
    
    $fp = fopen($pdfFilePath, 'rb');
    while (!feof($fp)) {
        echo fread($fp, 8192);
    }
    fclose($fp);
} else {
    echo "文件不存在或路径错误！";
}

$fileName = '测试文件.pdf';

header('Content-Type: application/pdf');
header('Content-Disposition: attachment; filename="' . urlencode($fileName) . '"');