<form action="" method="post" enctype="multipart/form-data">
    <p>File:&nbsp;<input name="file" type="file" /></p>
    <p><input name="submit" type="submit" value="Parse" /></p>
</form>
<?php

if(isset($_POST['submit'])) {

    define('ROOT_DIR', dirname(__FILE__) . '/');

    $valid_extensions = array('txt');

    if($_FILES['file']['error'] === UPLOAD_ERR_OK) {
        $file_extension = pathinfo($_FILES['file']['name'], PATHINFO_EXTENSION);
        if(in_array($file_extension, $valid_extensions)) {
            $filename = substr(md5(date(His)), 5, 5) . '_' . $_FILES['file']['name'];
            $filename = trim($filename);
            if(move_uploaded_file($_FILES['file']['tmp_name'], $filename)) {
                $file = file($filename);
                $array = array();
                foreach($file as $line) {
                    $array[] = 'старт' . base64_encode ($line);
                }
                $fp = fopen($filename, "w");
                foreach($array as $line) {
                    fwrite($fp, $line."\r\n");
                }
                echo '<a href="' . $filename . '">' . $filename . '</a>';
            }
            else
                $info = 'Error #1';
        }
        else
            $info = 'Error #2';
    }
}
?>