How can we Give Sourse To I frmae control if Our Path Is out side our porjects.

you can create aspx page to render html by reading the content of given path. for example

protected void Page_Load(object sender, EventArgs e)
{
    string file = Request.QueryString["file"];
    Response.Write(File.ReadAllText(Path.Combine(@"D:\share", file)));
}

we send file name to this page as QueryString and we can read the file from some other drive and write to response.
now we have page which can give as src property of ifram like below

<iframe id="if1" runat="server" src="Default.aspx?file=HTMLPage1.htm"></iframe>