Using mail merge in asp.net

Microsoft.Office.Interop.Word.Application wordApp = new Microsoft.Office.Interop.Word.Application();

wordApp.Visible = false;
wordApp.ScreenUpdating = false;//Will speed up the process

object filename = path; // input

// file to
object newFileName = @"~\Quotation\Quotation\document_to_read_tomorrow1.pdf"; // output
object missing = System.Type.Missing;

Microsoft.Office.Interop.Word.Document doc = wordApp.Documents.Add(Template: filename);

foreach (Microsoft.Office.Interop.Word.Field field in doc.Fields)
{

	string fieldName =GetFieldName( field.Code.Text);
	if (dataToWrite.ContainsKey(fieldName))
	{
		field.Select();
		string value = dataToWrite[fieldName].ToString();
		wordApp.Selection.TypeText(value);
	}
}

// formt to save the file, this case PDF
object formatoArquivo = Microsoft.Office.Interop.Word.WdSaveFormat.wdFormatPDF;

// changes in paper size

doc.PageSetup.PaperSize = Microsoft.Office.Interop.Word.WdPaperSize.wdPaperA4;

// changes orietation paper
doc.PageSetup.Orientation = Microsoft.Office.Interop.Word.WdOrientation.wdOrientPortrait;

// other changes
//doc.PageSetup.LeftMargin = 20;
//doc.PageSetup.RightMargin = 0;


// save file

doc.SaveAs(ref newFileName, ref formatoArquivo, 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);

//doc.Close(ref missing, ref missing, ref missing);

object saveChanges = WdSaveOptions.wdDoNotSaveChanges;
((_Document)doc).Close(ref saveChanges, ref missing, ref missing);
doc = null;


// word has to be cast to type _Application so that it will find
// the correct Quit method.
((_Application)wordApp).Quit(ref missing, ref missing, ref missing);
wordApp = null;
return newFileName.ToString();

Could not load file or assembly 'Microsoft.Office.Interop.Word, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' or one of its dependencies. The system cannot find the file specified.

Retrieving the COM class factory for component with CLSID {000209FF-0000-0000-C000-000000000046} failed due to the following error: 80040154.