Excel to pdf using interop

I am converting excel file to pdf using interop. and i have a working code. but before saving it to pdf. it prompt a dialog box which ask the user to "save changes to the file or not" how can i avoid this prompt? and how can i close the excel when saving is done? Thank you ``` public string ExceltoPdf(string excelLocation, string outputLocation) { try { Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.Application(); app.Visible = false; Microsoft.Office.Interop.Excel.Workbook wkb = app.Workbooks.Open(excelLocation); wkb.ExportAsFixedFormat(Microsoft.Office.Interop.Excel.XlFixedFormatType.xlTypePDF, outputLocation); wkb.Close(); app.Quit(); return outputLocation; } catch (Exception ex) { Console.WriteLine(ex.StackTrace); throw ex; } } ```