Calculation in Acrobat Pro disappears when transfered to Adobe Sign

I have a purchase order form with a calculation of the total price. I've made text boxes for the price of each product (formatted as number with currency prefix) and one text box (same format) with a very easy calculation for price*units (as in dropdown). It works like a charm and looks pretty good with the format (see attachment 1), but when I go to Adobe Sign and try to send the file, all format is cleared and the calculation doesn't work. What can I do?

Thanks for your help!

/Medea