Is there a way to add an additional box to the bill template, so that I can add our Companies PO # ?

Hi there, 

It's good to customize your bill template so your business can stand out. Don't worry, I'll assist you by sharing more info on this. At this time, you can only customize an Invoice, Estimate and Sales Receipt. I recommend manually adding the PO # each time you create a bill. Here's an screenshot of where you can add the PO #:

I encourage you to send feedback about this to our engineers. You can do this by clicking the gear icon and looking for Feedback. New product developments are based on the great feedback we get from users like you. Feel free to ask questions. I'm here to help. :)