The procedure for adding Microsoft Office Interop Excel Dll library depends on whether you are using Windows 7 or Windows 8/8.1/10. Follow these steps:
1. Open Windows Explorer from the Windows Start menu or from the desktop by pressing Windows+E keys together. 2. On the View tab, select Details from the Navigation Pane menu. This will open a new window with information about the selected file or folder. 3. From the details window, right-click on Microsoft Office Interop Excel Dll library file and select Add to select it from the list of libraries in the Choose Additions dialog box.