Auto-Calculating PDF Work Order

I’ve built a fillable work-order PDF for my team and now I want it to do the math for us. The form already has fields for Quantity, Unit Price, Subtotal, Tax, Total, and Discount, but they’re all static. I need simple addition and subtraction logic inserted so that:

• each line item multiplies Quantity by Unit Price,
• those subtotals roll up automatically,
• tax is applied, any discount is deducted,
• and the grand total refreshes the moment any number changes—no extra button clicks.

Please edit the existing PDF (Adobe Acrobat JavaScript or equivalent form-field calculations are fine) and return a fully functional file plus a brief note explaining where the scripts live in case I need to tweak them later. Everything should work seamlessly in standard desktop Acrobat and the free Acrobat Reader.