How Can I Add Folder Browser Inside A Combobox In C# ?

That dropdown is opening a treview node file. For this first you have to make one treeview combobox.
Then you will bind system direcotory list.
We are providing some part solution to make you a good solution from your side
First combobox with treeview
http://www.brad-smith.info/blog/archives/193[^]
http://demos.telerik.com/aspnet-ajax/treeview/examples/functionality/treeviewcombobox/defaultcs.aspx[^]


Get the system directory to bind on this combobox

void ListDirectory()
{
    treeView1.Nodes.Clear();
    var rootDirectoryInfo = new DirectoryInfo(txtPath.Text);
    treeView1.Nodes.Add(CreateDirectoryNode(rootDirectoryInfo));
    LoadFileDetails("");
}
TreeNode CreateDirectoryNode(DirectoryInfo directoryInfo)
{
    var directoryNode = new TreeNode(directoryInfo.Name);
    try
    {
        foreach (var directory in directoryInfo.GetDirectories())
        {
            directoryNode.Nodes.Add(CreateDirectoryNode(directory)); 
        } 
    }
    catch (UnauthorizedAccessException) { }
    catch (Exception) { }
    return directoryNode;
}