First, I create a new project within Visual Studio .NET and add a reference to the Microsoft Word type library. I am using Microsoft Word 2003, so the type library is Microsoft Word 11.0 Object Library. Once the reference is added, I can use the Word objects in the code.

Imports System.Runtime.InteropServices
Imports Microsoft.Office.Interop.Word

Public Class Form1 Inherits System.Windows.Forms.Form

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim strFileName As String
Dim word As New Microsoft.Office.Interop.Word.Application
Dim doc As Microsoft.Office.Interop.Word.Document

Try
doc = word.Documents.Open("c:\test.doc")
doc.Activate()
Catch ex As COMException
MessageBox.Show("Error accessing Word document.")
End Try
End Sub

End Class

(this is use for open word only so how to put inside textbox?)

* The System.Runtime.InteropServices namespace is imported to work with COM and .NET interoperability. It contains the COMException class.
* The .NET wrapper for the Word objects is contained in the Microsoft.Office.Interop.Word namespace (the reference previously added to the project).
* The Application class within the Word namespace is used to access the Word application.
* The Document class within the Word namespace allows you to work with Word documents.
* The Open method contained within the Documents property of the application allows an existing document to be loaded. It contains a Close method as well.
* The Activate method of the Document class opens the document within a new instance of Word.
* The code accessing the Word document is contained within a Try/Catch block. It catches COM errors via the COMException class.
* The MessageBox.Show method replaces the Office VBA MsgBox function.