One of the data types that you are able to export to a Custom PDF Output is Recent Approval Name.
This option places the name of the admin who was the most recent (last) Reviewer who Approved a process to move forward from a specific step. Here's a short video that shows how to add the name of the most recent Reviewer to your Custom PDF Output.
This option is one of three mappable components of a Review step:
Signature from the Review group/ step (if signatures are enabled for that Review)
Approval date for each Review step and Review group
Recent Approval Name
Here's a screenshot to show how these options appear for mapping after you've uploaded a Custom PDF to use as the Output for a workflow.