Set password in Word Document using C# and VB.Net in Wondows Application

Hi PRA,

Check this example. Now please take its reference and correct your code.

Namespaces

C#

using Word = Microsoft.Office.Interop.Word;

VB.Net

Imports Word = Microsoft.Office.Interop.Word

Code

C#

private void btnSetPassword_Click(object sender, EventArgs e)
{
    Word._Application objApp = null;
    Word._Document objDoc = null;
    object fileToOpen = "D:\\Doc.docx";
    object objMiss = Type.Missing;
    objApp = new Word.Application();
    objDoc = objApp.Documents.Open(ref fileToOpen, ref objMiss, ref objMiss, ref objMiss, ref objMiss,
        ref objMiss, ref objMiss, ref objMiss, ref objMiss, ref objMiss, ref objMiss,
        ref objMiss, ref objMiss, ref objMiss, ref objMiss, ref objMiss);

    try
    {
        objDoc.Password = txtPassword.Text; //set password to open file.
        objDoc.ReadOnlyRecommended = false;
        objDoc.Save(); //save word document.
        MessageBox.Show("Word locked successfully !", "Word Protect", MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message, "Word Protect", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

VB.Net

Private Sub btnSetPassword_Click(sender As System.Object, e As System.EventArgs) Handles btnSetPassword.Click
    Dim objApp As Word._Application = Nothing
    Dim objDoc As Word._Document = Nothing
    Dim fileToOpen As Object = "D:\Doc.docx"
    Dim objMiss As Object = Type.Missing
    objApp = New Word.Application()
    objDoc = objApp.Documents.Open(fileToOpen, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss, objMiss)

    Try
        objDoc.Password = txtPassword.Text
        objDoc.ReadOnlyRecommended = False
        objDoc.Save()
        MessageBox.Show("Word locked successfully !", "Word Protect", MessageBoxButtons.OK, MessageBoxIcon.Information)
    Catch ex As Exception
        MessageBox.Show(ex.Message, "Word Protect", MessageBoxButtons.OK, MessageBoxIcon.[Error])
    End Try
End Sub

Refer below link for more details.

https://www.codeproject.com/Articles/1058951/Protect-word-document-using-Csharp-and-Word-Automa