how can we open Ms word in C# Windows application ?

If you just want to open MS Word application then you can do this:

System.Diagnostics.Process.Start(@"Winword.exe");

If you want to have an actual editor in your applications then see this:
https://code.msdn.microsoft.com/Word-Document-Editor-in-d97fd70b
The sample uses this word processing library for .NET.
You can check here various C# manipulations on DOCX documents that can be achieved with it.

There are three main ways to work with Word documents in c#:

1) Use Office Interop:

http://www.mindstick.com/Articles/5cd1b721-9b94-4ea0-bd6e-2bb157401069/
http://zirmandli.wordpress.com/2007/07/04/read-word-doc-using-c/
http://www.4microsoftsolutions.com/post/Create-Open-Microsoft-Word-Document-in-C.aspx
http://nishantrana.wordpress.com/2007/11/03/creating-word-document-using-c/

2) If you work with .docx format only you may use OpenXML:

http://www.microsoft.com/en-us/download/details.aspx?id=5124
http://www.c-sharpcorner.com/Blogs/9051/
http://somecodesnippets.blogspot.ru/2012/05/how-to-create-word-document-with-c.html

3) You may use some 3rd party .Net components. For example look at this C# Word component

Use below code:

private void btnOpen_Click(object sender, EventArgs e)

        {

            //Open a Doc Document

            OpenFileDialog dialog = new OpenFileDialog();

            dialog.Filter="Word97-2003 files(*.doc)|*.doc|Word2007-2010 files (*.docx)|*.docx|All files (*.*)|*.*";

            dialog.Title="Select a DOC file";

            dialog.Multiselect=false;

            dialog.InitialDirectory = System.IO.Path.GetFullPath(@"..\word to image.doc");          

          

            DialogResult result = dialog.ShowDialog();

            if (result==DialogResult.OK)

            {

                try

                {

                    // Load doc document from file.

                    this.docDocumentViewer1.LoadFromFile(dialog.FileName);

                    this.textBox2.Text = this.docDocumentViewer1.PageCount.ToString();

                }

                catch (Exception ex)

                {

                    MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

                }

            }

        }

but you need to download a .NET DocViewer

Hi Vini,

Please refer the below links

http://www.c-sharpcorner.com/UploadFile/mgold/CreatingandOpeningMicrosoftDocumentfrom.NETUsingCSharp11262005050939AM/CreatingandOpeningMicrosoftDocumentfrom.NETUsingCSharp.aspx

http://www.codeproject.com/Articles/3959/Microsoft-Word-Documents-from-ASP-NET

Thanks