Found IT!!!! the below code will set the page number as a footer and place in center.
************************************************************************************
var Box2Width = 50;
for (var p = 0; p < openDoc.numPages; p++) {
var aRect = openDoc.getPageBox("Crop",p);
var TotWidth = aRect[2] - aRect[0];
var bStart=(TotWidth/2)-(Box2Width/2);
var bEnd=((TotWidth/2)+(Box2Width/2));
var fp = openDoc.addField(String("xftPage"+p+1), "text", p, [bStart,30,bEnd,15]);
fp.value = "String(p+1);
fp.textSize = 6;
fp.readonly = true;
fp.alignment="center";
}
*********************************************************************************************
Full Example = Adobe Acrobat 9 Javascript to add footer to document - Stack Overflow