Are you copying text out of an ezMerge template?

YES

1. Create an HTML field on your order form. Name it anything you'd like.

2. Copy/Paste the following code into the new HTML field. Be sure to replace udf_NameOfAEMFieldOnForm, NameOfAEMField, and udf_FieldToBeAutoFilled below.

<script type="text/javascript">
<!--
$(document).ready(function(){
     function CopyText() {
          $('#udf_FieldToBeAutoFilled').val($('#udf_NameOfAEMFieldOnForm\\:NameOfAEMField').val());
     }
     $('#udf_NameOfAEMFieldOnForm\\:NameOfAEMField').bind('change', function(e) { CopyText(); });
     CopyText();
});
-->
</script>

For multiple fields into one, just add additional bind functions into $(document).ready and add the field(s) into the filled field's val() like so:

<script type="text/javascript">
<!--
$(document).ready(function(){
     function CopyText() {
          $('#udf_FieldToBeAutoFilled').val($('#udf_NameOfAEMFieldOnForm\\:NameOfAEMField1').val() + ' ' +
          $('#udf_NameOfAEMFieldOnForm\\:NameOfAEMField2').val());
     }
     $('#udf_NameOfAEMFieldOnForm\\:NameOfAEMField1').bind('change', function(e) { CopyText(); });
     $('#udf_NameOfAEMFieldonForm\\:NameOfAEMField2').bind('change', function(e) { CopyText(); });  
     CopyText();
});
-->
</script>

NO

1. Follow the instruction above, but Copy/Paste the following code into the field new HTML field. Be sure to replace udf_FieldToBeCopied and udf_FieldToBeAutoFilled below.

<script type="text/javascript"> 
<!-- 
$(document).ready(function(){
     function CopyText() {
          $('#udf_FieldToBeAutoFilled').val($('#udf_FieldToBeCopied').val());
     } 
     $('#udf_FieldToBeCopied').bind('change', function(e) { 
          CopyText();
     });
     CopyText();
}); 
 --> 
 </script>