Have you tried Options | Customize | Menus | Default Menu: Reset ?
If that doesn't work, go to Options | Customize | Commands, select 'File' in the left panel, then scroll the right panel until "Open With" comes into view. Drag and drop it onto your File menu between Edit and Edit Metadata (give the File menu a second to expand while you hover your cursor over it). Finally, click Close on the Customize dialog.