I am trying to create an interactive PDF that uses formulas from an Excel tax calculator that we have created
Our graphic designer sent me a half completed project. He can not seem to transfer the actual formulas from the Excel spreadsheet into the fields of the PDF to calculate.
Once you (or your designer) have the completed design of the PDF, to make it interactive (with formulas), that is not to be done in InDesign. To make a form, see suggestion here: Creating an indesign fillable form with computation (addition)