how to view file content in textbox?

You can read uploaded file inputsteam into a stream object then using streamreader read and append lines in a string builder at the end of loop display string builder content in a texbox like this:

<table>
          <tr>
              <td>
              </td>
              <td>
                  <asp:FileUpload ID="fileupload1" runat="server" />
              </td>
          </tr>
          <tr>
              <td>
              </td>
              <td>
                  <asp:Button ID="btnRead" runat="server" OnClick="btnRead_Click" Text="Read" />
              </td>
          </tr>
          <tr>
              <td valign="top">
                  Message of Created Text file :
              </td>
              <td>
                  <asp:TextBox ID="textBoxContents" runat="server" TabIndex="0" Height="380px" TextMode="MultiLine"
                      Width="367px"></asp:TextBox>
              </td>
          </tr>
      </table>

protected void btnRead_Click(object sender, EventArgs e)
        {
            string path = fileupload1.PostedFile.FileName;
            if (!string.IsNullOrEmpty(path))
            {

                Stream theStream = fileupload1.PostedFile.InputStream;
                StringBuilder strbuild = new StringBuilder();
                using (StreamReader sr = new StreamReader(theStream))
                {
                    string line;
                    while ((line = sr.ReadLine()) != null)
                    {
                        strbuild.Append(line);
                        strbuild.AppendLine();
                    }
                }
               
                textBoxContents.Text = strbuild.ToString();
            }

           
        }