The easiest way to do this is to record a macro in Word.
With your Excel file open, start Word and Tools/Macro/Record new macro.
Assign the macro to a keyboard function (e.g. CTRL+I).
Do all the actions necessary to transfer the information from Excel to Word. Then stop the macro recorder.
The next time you need to do this, make sure the Excel Workbook is open, start Word and press your keyboard shortcut.
A question - why? Wouldn't it be easier to print the invoice directly from Excel?