Merhaba, bir proje için php ile doc, docx, pdf uzantıları ile dosya upload etmem gerekiyor. Ancak sabahtan beri halledemedim. Nerede hata yapıyorum yardımcı olurmusunuz ? Sorun nerede ?

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<form action="upload.php" method="post" enctype="multipart/form-data">
    <input type="file" name="uploadthisfile" />
    <input type="submit" value="Upload" />
</form>
</body>
</html>
<?php
if(isset($_FILES['uploadthisfile']))
{
    if($_FILES['uploadthisfile']['error'] != 0)
    {
        if($_FILES['uploadthisfile']['size'] == 0)
            echo 'Please choose file.';
        else
            echo 'Error while uploading.';
    }
    else
    {
        if($_FILES['uploadthisfile']['size'] > (1024*1024*8))
            echo 'Maximum file size 8MB.';
        else
        {
            $myfiletype = $_FILES['uploadthisfile']['type'];
            $myfilename = $_FILES['uploadthisfile']['name'];
            $myfileextension = explode('.', $myfilename);
            $myfileextension = $myfileextension[count($myfileextension)-1];
            if($myfiletype != "application/pdf" && $myfiletype != "application/vnd.openxmlformats-officedocument.wordprocessingml.document" && $myfiletype != "application/msword" && $myfileextension != 'doc' && $myfileextension != 'docx' && $myfileextension != 'pdf')
                echo 'You can only upload DOC, DOCX, PDF files.';
            else
            {
                $uploadthisfile = $_FILES['uploadthisfile']['tmp_name'];
                copy($uploadthisfile, 'upload/' . $_FILES['uploadthisfile']['name']);
                echo 'File uploaded successfully.';
            }
        }
    }
}
?>