C# Word Styling Automation

ApplicationClass objWordApp = new ApplicationClass();
Document objWordDoc = new Document();         

foreach (string eachfile in lstfile.Items)
{
                Object nothing = System.Reflection.Missing.Value;
                Object fileName = txtFilename.Text.ToString();
                Object notTrue = false; 
                Object missing = System.Reflection.Missing.Value;
                objWordDoc = null;

                Object readOnly = false;
                Object isVisible = false;

                objWordApp.Visible = false;

                objWordDoc = objWordApp.Documents.Open(ref fileName, ref

missing,
                      ref readOnly, ref missing, ref missing, ref missing,
                      ref missing, ref missing, ref missing, ref missing,
                      ref missing, ref isVisible, ref missing, ref missing,
                      ref missing, ref missing);
                objWordDoc.Activate();
                objWordApp.Visible = false;

                string InDoc = OPagPath + "\\" + eachfile;
                objWordApp.Selection.InsertFile(PagFpath, ref missing, ref missing, ref

missing, ref missing);

   //Here I need help to find and replace with particular style
}

objWordApp.Quit(ref notTrue, ref missing, ref missing);