Saving temporary files in web applications

using System;
using System.Data;
using System.Configuration;
using System.Collections.Generic;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page 
{
    private List<DocumentFile> _documents
    {
        get
        {
            if (ViewState["Documents"] == null)
                ViewState["Documents"] = new List<DocumentFile>();
            return (List<DocumentFile>)ViewState["Documents"];
        }
        set
        {
            ViewState["Documents"] = value;
        }
    }
    
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
            DataBind();
    }

    public override void DataBind()
    {
        base.DataBind();
        grdDocuments.DataSource = _documents;
        grdDocuments.DataBind();
    }

    protected void lnkAddDocument_Click(object sender, EventArgs e)
    {
        if (IsValid)
        {
            TempUpload tempUpload = new TempUpload(fileDocument);
            String documentPath = tempUpload.SaveFile();
            _documents.Add(new DocumentFile(Guid.NewGuid().ToString(), txtDocumentTitle.Text, documentPath));
            DataBind();
            txtDocumentTitle.Text = String.Empty;
        }
    }

    protected void butAddFolder_Click(object sender, EventArgs e)
    {
        if (IsValid)
        {
            // 1. Insert Folder in table and get ID

            // 2. Using Folder ID insert All Uploaded Documents
            //    and move files from Temp folder to permanent storage

            foreach (DocumentFile document in this._documents)
            {

            }
        }
    }

    protected void grdDocuments_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        switch (e.CommandName)
        {
            case "DeleteDocument":
                foreach (DocumentFile document in _documents)
                {
                    if (document.ID.Equals(e.CommandArgument))
                    {
                        _documents.Remove(document);
                        break;
                    }
                }
                DataBind();
                break;
        }
    }
}