Read and display contents of HTML file on ASP.Net page

Refer:

1. Read HTML file and display it on ASP.Net Web Page

For selecting the files from the folder you need to make use of FileUpload control.

Please refer this code

HTML

<form id="form1" runat="server">
<div>
    <asp:FileUpload ID="fuFileUpload" runat="server" />
    <asp:Button Text="Upload and Display html File" OnClick="UploadDisplay" runat="server" />
    <br />
    <div id="dvHtml" runat="server">
    </div>
</div>
</form>

Namespace

using System.IO;

C#

protected void UploadDisplay(object sender, EventArgs e)
{
    if (this.fuFileUpload.HasFile)
    {
        this.fuFileUpload.PostedFile.SaveAs(Server.MapPath("~/HTMLFiles/" + Path.GetFileName(this.fuFileUpload.FileName)));
    }
    string body = string.Empty;
    using (System.IO.StreamReader reader = new System.IO.StreamReader(Server.MapPath("~/HTMLFiles/" + Path.GetFileName(this.fuFileUpload.FileName))))
    {
        dvHtml.InnerHtml = reader.ReadToEnd();
    }
}