You don't need designer to create the forms, it's just a nice applications (windows only) that creates them all for you including the automatic calculations.
On mac just use the normal Adobe Acrobat Application and under the menu Add? (Can't remember) just add a new form element.
It's easy on mac, but easier on windows. Both platforms support all the functionality, it's just that windows has a simplier "more mac like way" of laying out the forms and performing calculations.