Sending invoices to be annotated and signed - how?

Hi all, I am fairly new to Adobe DC as a school business manager trying to run operations remotely.

I need a quick way of sending different finance documents to be annotated and signed. 

Normally we would print off an invoice, stamp it with specific text/fields to complete (Cost centre, "I confirm receipt of good and services", Signature) plus they could add any comments. This would go internally to staff then returned for payment. I would like to replicate this by email. 

I have tried the fill and sign function which is good for collecting signatures, and I can drag comments boxes but I can't see where to write instructions. It's quite long-winded each time. We will be sending multiple documents for authorisation per day and ideally I would just like to overlay a small form, I just can't work out how.  Maybe there is a better way?

Many thanks