Cannot create an instance of an abstract class or interface Microsoft Office Interop Word Application

using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Printing;
using System.Text;
using System.Windows.Forms;
using Word = Microsoft.Office.Interop.Word;
using Office = Microsoft.Office.Core;
using System.Runtime.InteropServices;
using System.Threading;
 
 
 
 
try
                {
                    Microsoft.Office.Interop.Word.Application word = null; Microsoft.Office.Interop.Word.Document doc = null;
                    word = new Microsoft.Office.Interop.Word.Application();
                    
                    object missing = System.Type.Missing;
                    string filen;
                    filen = @"c:\\Complaints\\" + this.lnTextBox.Text + "_" + this.fnTextBox.Text + ".docx";
                    object fileName = filen;
                    object falseValue = false;
                    object trueValue = true;
                   
                    word.Visible = true;
                    word.Activate();
                    doc = word.Documents.Add(ref missing, ref missing, ref missing, ref trueValue);
                    string wordcleaning;
                    wordcleaning = "HISTORY OF ILLNESS:\n\n";
 
                    Word.Range range = null;
                    object startPosition = 0;
                    object endPosition = 0;
                    range = doc.Range(ref startPosition, ref endPosition);
                    range.Text = insertText;
                    doc.SaveAs(ref fileName, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
                }
                catch (System.Runtime.InteropServices.COMException exword3) { MessageBox.Show("Error accessing Word document."); }

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