What event does calculation?

You have a typo, and for numerical addition you should explicitly convert the field values to numbers so you don't get string concatenation in the case of empty fields. You can convert to a number using the unary + operator. Try this:

var a = +getField("fldYesYellowEnvelope").value;
var b = +getField("fldYesWhiteEnvelope").value;
var c = +getField("fldCurrentPVBMCount").value;

event.value = a + b + c;

or better yet:

(function () {

var a = +getField("fldYesYellowEnvelope").value;
var b = +getField("fldYesWhiteEnvelope").value;
var c = +getField("fldCurrentPVBMCount").value;

event.value = a + b + c;

})();

...to prevent the unnecessary creation of document-global variables.

If you are using LiveCycle Designer you can also use the FormCalc code:

fldYesYellowEnvelope + fldYesWhiteEnvelope + fldCurrentPVBMCount

Are you getting and error messages?

In "Preview" open the JavaScript Debugging console of Acroaat with the key combination " + J"

I get this error:

script failed (language is formcalc; context is xfa.

Error: access 'fldYesYellowEnvelope' is unknown

Your original code was for a form created in Acrobat, not LiveCycle Designer. That's the reason your code isn't working. You can use FormCalc as suggested above, or learn the equivalent JavaScript for XFA. There are several tutorials here that should help.

You could also change the scripting language to "JavaScript" within LiveCycle Designer. And use the follwing script:

var a = fldYesYellowEnvelope.rawValue;
var b = fldYesWhiteEnvelope.rawValue;
var c = fldCurrentPVBMCount.rawValue;
event.rawValue = a + b + c;

This worked:

IFS.Page5.fldVbmEnvelopeOrderQty0 = IFS.Page4.fldYesYellowEnvelope + IFS.Page5.fldYesWhiteEnvelope + IFS.Page4.fldCurrentPVBMCount;


Data Format has to be an interger not float for every field.

Had to reference the document name and page number and field.

This is a FormCalculation. Hope this helps out someone in the future.