The sample demonstrates how to Set bookmark in Word document.

private void button1_Click(object sender, EventArgs e)
{
    //Create word document
    Document document = new Document();

    Bookmark(document.AddSection());

    //Save doc file.
    document.SaveToFile("Sample.doc",FileFormat.Doc);

    //Launching the MS Word file.
    WordDocViewer("Sample.doc");


}

private void Bookmark(Section section)
{
    Paragraph paragraph = section.AddParagraph();
    paragraph.AppendText("The sample demonstrates how to using bookmark.");
    paragraph.ApplyStyle(BuiltinStyle.Heading2);

    section.AddParagraph();
    paragraph = section.AddParagraph();
    paragraph.AppendText("Simple bookmark.");
    paragraph.ApplyStyle(BuiltinStyle.Heading4);
    
    // Writing simple bookmarks
    section.AddParagraph();
    paragraph = section.AddParagraph();
    paragraph.AppendBookmarkStart("SimpleBookMark");
    paragraph.AppendText("This is a simple book mark.");
    paragraph.AppendBookmarkEnd("SimpleBookMark");

    section.AddParagraph();
    paragraph = section.AddParagraph();
    paragraph.AppendText("Nested bookmark.");
    paragraph.ApplyStyle(BuiltinStyle.Heading4);

    // Writing nested bookmarks
    section.AddParagraph();
    paragraph = section.AddParagraph();
    paragraph.AppendBookmarkStart("Root");
    paragraph.AppendText(" Root data ");
    paragraph.AppendBookmarkStart("NestedLevel1");
    paragraph.AppendText(" Nested Level1 ");
    paragraph.AppendBookmarkStart("NestedLevel2");
    paragraph.AppendText(" Nested Level2 ");
    paragraph.AppendBookmarkEnd("NestedLevel2");
    paragraph.AppendText(" Data Level1 ");
    paragraph.AppendBookmarkEnd("NestedLevel1");
    paragraph.AppendText(" Data Root ");
    paragraph.AppendBookmarkEnd("Root");

}

private void WordDocViewer(string fileName)
{
    try
    {
        System.Diagnostics.Process.Start(fileName);
    }
    catch { }
}

Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles button1.Click
	'Create word document
	Dim document_Renamed As New Document()

	Bookmark(document_Renamed.AddSection())

	'Save doc file.
	document_Renamed.SaveToFile("Sample.doc",FileFormat.Doc)

	'Launching the MS Word file.
	WordDocViewer("Sample.doc")


End Sub

Private Sub Bookmark(ByVal section_Renamed As Section)
	Dim paragraph_Renamed As Paragraph = section_Renamed.AddParagraph()
	paragraph_Renamed.AppendText("The sample demonstrates how to using bookmark.")
	paragraph_Renamed.ApplyStyle(BuiltinStyle.Heading2)

	section_Renamed.AddParagraph()
	paragraph_Renamed = section_Renamed.AddParagraph()
	paragraph_Renamed.AppendText("Simple bookmark.")
	paragraph_Renamed.ApplyStyle(BuiltinStyle.Heading4)

	' Writing simple bookmarks
	section_Renamed.AddParagraph()
	paragraph_Renamed = section_Renamed.AddParagraph()
	paragraph_Renamed.AppendBookmarkStart("SimpleBookMark")
	paragraph_Renamed.AppendText("This is a simple book mark.")
	paragraph_Renamed.AppendBookmarkEnd("SimpleBookMark")

	section_Renamed.AddParagraph()
	paragraph_Renamed = section_Renamed.AddParagraph()
	paragraph_Renamed.AppendText("Nested bookmark.")
	paragraph_Renamed.ApplyStyle(BuiltinStyle.Heading4)

	' Writing nested bookmarks
	section_Renamed.AddParagraph()
	paragraph_Renamed = section_Renamed.AddParagraph()
	paragraph_Renamed.AppendBookmarkStart("Root")
	paragraph_Renamed.AppendText(" Root data ")
	paragraph_Renamed.AppendBookmarkStart("NestedLevel1")
	paragraph_Renamed.AppendText(" Nested Level1 ")
	paragraph_Renamed.AppendBookmarkStart("NestedLevel2")
	paragraph_Renamed.AppendText(" Nested Level2 ")
	paragraph_Renamed.AppendBookmarkEnd("NestedLevel2")
	paragraph_Renamed.AppendText(" Data Level1 ")
	paragraph_Renamed.AppendBookmarkEnd("NestedLevel1")
	paragraph_Renamed.AppendText(" Data Root ")
	paragraph_Renamed.AppendBookmarkEnd("Root")

End Sub

Private Sub WordDocViewer(ByVal fileName As String)
	Try
		Process.Start(fileName)
	Catch
	End Try
End Sub