YA: SimpleFileUploadChecking

<?php
// Upload Errors ** NOTE: There is no error number 5. It was an old error, removed. **
$uploadErrors = array(
    1 => 'The uploaded file exceeds the Server\'s Maximum Allowable File Size',
    2 => 'The uploaded file exceeds the Form\'s Maximum Allowable File Size.',
    3 => 'The uploaded file was only partially uploaded, then interrupted or the connection was dropped.',
    4 => 'No file was uploaded.',
    6 => 'Missing a temporary folder. The server requires a temporary folder for file uploads.', // Internal Operations Error
    7 => 'Failed to write file to disk.', // Internal Server Error
    8 => 'A PHP extension stopped the file upload.' // PHP Extension Library stopped the upload.
);
$allowableFileExts = Array('pdf'); // Allowed file extensions, extensions and content-types can be spooffed. So it's not a hundred percent.
// Functions
function cleanString($s){
    // To help protect from MySQL Injection attacks. Not 100% but better than nothing.
    if(get_magic_quotes_gpc()){
        return mysql_real_escape_string(stripslashes($s));
    }else{
        return mysql_real_escape_string($s);
    }
}
function logDetails($title,$description,$content_type,$target){
    $text = 'Time: ' . date('D M j, Y @ H:i:s [e]') . '(Server Time)' . PHP_EOL;
    $text .= 'Title: ' . $title . PHP_EOL;
    $text .= 'Description: ' . $description . PHP_EOL;
    $text .= 'Content-Type: ' . $content_type . PHP_EOL;
    $text .= 'Server Filename (target): ' . $target . PHP_EOL;
    $text .= str_pad('', 60, '_') . PHP_EOL;
    $fh = fopen('log_databaseInputFails.txt','a');
    fwrite($fh,$text);
    fclose($fh);
}

// Processing
if($_FILES['content_file']['error'] !== UPLOAD_ERR_OK){ // If the upload's error is not 0 or Upload Ok
    die('There was an error uploading the file.<br />Error: ' . $uploadErrors[$_FILES['content_file']['error']]);
}else{
    $ext = pathinfo($_FILES['content_file']['name'], PATHINFO_EXTENSION) ;
    if( !in_array($ext, $allowableFileExts)){
        die('This file type is not permitted');
    }
    $conn = mysql_connect("..........") or die(mysql_error()) ;
    mysql_select_db(".......") or die(mysql_error()) ;

    while(file_exists(($target = "files/" . rand() . '.' . $ext))){}; // If the file exists, then it will try another file name. Otherwise you could get files over written onto other files.

    $title = cleanString($_POST['title']);
    $description = cleanString($_POST['description']);
    $content_type = cleanString($_POST['content_type']);
    $content_file = cleanString($_FILES['content_file']['tmp_name']);

    // You need to be storing the $target in your database as well.
    // $semester ??? Should that be $description ???
    $result = mysql_query("INSERT INTO `materials` VALUES ('$title', '$description', '$content_type', '$target')") ;
    $moved = move_uploaded_file($content_file, $target);

    if($result && $moved){
        // The Data has been Added to the Database and the upload was stored successfully.
        echo "The file " . basename( $_FILES['uploadedfile']['name']) . " has been uploaded, and your information has been added to the directory";
    }else if($result && !$moved){
        // Data Added, but error with file.
        mysql_query("DELETE FROM materials WHERE title='{$title}' LIMIT 1");
        echo 'There was an error Uploading your file, please try again.';
    }else if (!$result && $moved){
        // The File has been uploaded successfully, but not added to the database. Log details for admin addition to the database.
        logDetails($title,$description,$content_type,$target);
        echo "The file " . basename( $_FILES['uploadedfile']['name']) . " has been uploaded, but has yet to be added to the database. It will be added once the Database is online.";

    } else {
        echo "Sorry, there was a problem completing the uploading of your file. Please Try Again Later.";
    }
}
?>

The display script:

<?php
mysql_connect("...........") or die(mysql_error()) ;
mysql_select_db("..........") or die(mysql_error()) ;

$data = mysql_query("SELECT * FROM materials") or die(mysql_error());

while($info = mysql_fetch_array( $data )){
    echo '<a href="http://www.mysite.com/files/' . $info['target'] . '">' . $info['title'] . "</a> <br>";
    echo "<b>Description:</b> " . $info['description'] . " <br>";
    echo "<b>Content Type:</b> " . $info['content_type'] . " <hr>";
}
?>