文件名是由采购订单+发票在sql表中生成的。当用户附加一个pdf文件时，它会覆盖具有相同采购订单+发票的现有文件名。无论如何，我可以创建唯一ID文件名吗？

public partial class upload : System.Web.UI.Page
{
    string mID;

    DataBaseDataContext dataBaseDataContext = new DataBaseDataContext();
    protected void Page_Load(object sender, EventArgs e)
    {
    }

    protected void btnExit_Click(object sender, EventArgs e)
    {
        Response.Redirect("Default.aspx");
    }

    protected void SUbmit(object sender, EventArgs e)
    {
        try
        {
            var ext = FileUploadtoServer.FileName.Substring(FileUploadtoServer.FileName.IndexOf('.') + 1, 3);
            if (ext.ToLower() != "pdf")
            {
                Response.Write("<script>alert('Please select a pdf File!')</script>");
                return;
            }
        }
        catch (Exception ex)
        {
            Response.Write("<script>alert('Please select a pdf File!')</script>");
            return;
        }

        if (PO_Number.Text.Equals("") || HeadCode.Text.Equals("") || Manufacture.Text.Equals("") || Description.Text.Equals("") || Invoice.Text.Equals(""))
        {
            Response.Write("<script>alert('Please Fill All Fields!')</script>");
        }

        TPT tPT = new TPT();
        tPT.Invoice_No = Invoice.Text;
        tPT.PO_Number = PO_Number.Text;
        tPT.Item_Code = Manufacture.Text;
        tPT.Heat_Code = HeadCode.Text;
        tPT.Description = Description.Text;
        tPT.FileName = PO_Number.Text + Invoice.Text + ".pdf";
        dataBaseDataContext.TPTs.InsertOnSubmit(TPT);
        dataBaseDataContext.SubmitChanges();

        String path = Server.MapPath("Attachments/" + PO_Number.Text + Invoice.Text + ".pdf");
        FileUploadtoServer.SaveAs(path);
        Response.Write("<script>alert('Successfully Inserted!')</script>");
        Invoice.Text = "";
        Manufacture.Text = "";
        HeadCode.Text = "";
        Description.Text = "";
        PO_Number.Text = "";
    }
}

我试过了

Guid.NewGuid() + ".pdf";,

它仍然做同样的事情。