@Kovah, Thank you for the link; But it does not seem to be helping on the PDF for the Custom Fields.
I use like this as shown below, but it does not display the Value of the Custom Field, instead throws an error.
Request to please suggest/help on this.
I am using Invoice Plane 1.5.2
Just realized after reading the code over and over again after a good night sleep and some coffee.
I had not echo-ed the values out, to add to the entertainment, I had a typo in it as well.
Corrected as below and it works like a charm. Thank you @Kovah for the clean documentation. <?php echo $custom_fields['user']['PanID'] ?>