In this article I will explain with an example, how to convert Microsoft office Word Document i.e. (DOC and DOCX) files to HTML and also display it in browser in ASP.Net using C# and VB.Net.
The Word document will be first uploaded, then it will be converted to HTML using Microsoft Office Interop Library and finally the converted HTML will be displayed in web page in ASP.Net using C# and VB.Net.
Adding reference of Microsoft Office Interop Library
In order to add reference of the Microsoft Office Interop Library, right click on the Project in Solution Explorer and click Add Reference.
Then from the following Window, please select Microsoft Office Interop.Word assembly.
Convert Office Word Document to HTML and display it in browser in ASP.Net
HTML Markup
The following HTML Markup consists of an ASP.Net FileUpload control, a Button and an HTML DIV.
<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="btnUpload" runat="server" Text="submit" OnClick="Upload" />
<hr />
<div id="dvWord" runat="server"></div>

You will need to import the following namespaces.
using System.IO;
using Microsoft.Office.Interop.Word;
using System.Text.RegularExpressions;
Imports System.IO
Imports Microsoft.Office.Interop.Word
Imports System.Text.RegularExpressions
Convert Office Word Document to HTML and display it in browser in ASP.Net
The following event handler gets called when the Submit button is clicked.
The uploaded Word Document file is first saved into a Folder named Temp within the Project Folder and then the Word Document file is converted into HTML string using Microsoft Office Interop Library.
Finally the HTML string will be assigned to the InnerHtml property of the HTML DIV.
protected void Upload(object sender, EventArgs e)
    object documentFormat = 8;
    string randomName = DateTime.Now.Ticks.ToString();
    object htmlFilePath = Server.MapPath("~/Temp/") + randomName + ".htm";
    string directoryPath = Server.MapPath("~/Temp/") + randomName + "_files";
    object fileSavePath = Server.MapPath("~/Temp/") + Path.GetFileName(FileUpload1.PostedFile.FileName);
    //If Directory not present, create it.
    if (!Directory.Exists(Server.MapPath("~/Temp/")))
    //Upload the word document and save to Temp folder.
    //Open the word document in background.
    _Application applicationclass = new Application();
    applicationclass.Documents.Open(ref fileSavePath);
    applicationclass.Visible = false;
    Document document = applicationclass.ActiveDocument;
    //Save the word document as HTML file.
    document.SaveAs(ref htmlFilePath, ref documentFormat);
    //Close the word document.
    //Read the saved Html File.
    string wordHTML = System.IO.File.ReadAllText(htmlFilePath.ToString());
    //Loop and replace the Image Path.
    foreach (Match match in Regex.Matches(wordHTML, "<v:imagedata.+?src=[\"'](.+?)[\"'].*?>", RegexOptions.IgnoreCase))
        wordHTML = Regex.Replace(wordHTML, match.Groups[1].Value, "Temp/" + match.Groups[1].Value);
    //Delete the Uploaded Word File.
    dvWord.InnerHtml = wordHTML;
Protected Sub Upload(ByVal sender As Object, ByVal e As EventArgs)
    Dim documentFormat As Object = 8
    Dim randomName As String = DateTime.Now.Ticks.ToString
    Dim htmlFilePath As Object = Server.MapPath("~/Temp/") & randomName + ".htm"
    Dim directoryPath As String = Server.MapPath("~/Temp/") & randomName + "_files"
    Dim fileSavePath As Object = Server.MapPath("~/Temp/") & Path.GetFileName(FileUpload1.PostedFile.FileName)
    'If Directory not present, create it.
    If Not Directory.Exists(Server.MapPath("~/Temp/")) Then
    End If
    'Upload the word document and save to Temp folder.
    'Open the word document in background.
    Dim applicationclass As _Application = New Application
    applicationclass.Visible = False
    Dim document As Document = applicationclass.ActiveDocument
    'Save the word document as HTML file.
    document.SaveAs(htmlFilePath, documentFormat)
    'Close the word document.
    'Read the saved Html File.
    Dim wordHTML As String = System.IO.File.ReadAllText(htmlFilePath.ToString)
    'Loop and replace the Image Path.
    For Each match As Match In Regex.Matches(wordHTML, "<v:imagedata.+?src=[""'](.+?)[""'].*?>", RegexOptions.IgnoreCase)
        wordHTML = Regex.Replace(wordHTML, match.Groups(1).Value, ("Temp/" + match.Groups(1).Value))
    'Delete the Uploaded Word File.
    dvWord.InnerHtml = wordHTML
End Sub
Convert Office Word Document to HTML and display it in browser in ASP.Net