Drag and Drop only PDF files
<p>I have the following code that list the files that i drag  in a listbox. 
now i need to filter so it can only list PDF files and discard the rest. </p>

<pre><code>private void Form1_Load(object sender, EventArgs e)
{
    listBoxFiles.AllowDrop = true;
    listBoxFiles.DragDrop += listBoxFiles_DragDrop;
    listBoxFiles.DragEnter += listBoxFiles_DragEnter;
}

private void listBoxFiles_DragEnter(object sender, DragEventArgs e)
{
    if (e.Data.GetDataPresent(DataFormats.FileDrop))
        e.Effect = DragDropEffects.Copy;
}

private void listBoxFiles_DragDrop(object sender, DragEventArgs e)
{
    string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
    foreach (string file in files)
        listBoxFiles.Items.Add(file);
}
</code></pre>