Conditional Content in Transaction Receipts

I'm trying to set up a PDF receipt template with conditional content - I've seen some other threads but no solutions. 


One of the things I need to do, is display different content if it's an organizational gift vs. a constituent gift.   I have two hidden fields, one with organization_name and one with full_name - I then have another field where I wrote a custom calculation script that says if the organization_name field value is empty, use the value of full_name, otherwise use the value of organization_name.  Functionaly it works fine if I open up the PDF on my desktop and manually enter content (after I un-hide the hidden fields) - when I publish the template in LO and issue a receipt, no data is displayed in the field. 


Does anyone know how LO processes the PDF?   Is there a better way of doing this? 


Thanks,

Richard