Add "Customer" field to a custom PDF transaction layout

The field ID for the Customer is {entity}.

1. Navigate to  Customization > Forms > Transaction Form PDF Layouts. Locate PDF-Layout you wish to use. Click Edit.
2. Click Add a Custom Element > select Entity from the list.
3. Save the layout and test to see if the issue is resolved.

This is an alternate solution to the enhancement Issue #200147 - Setup> Customization> Transaction PDF Layouts> Standard Transaction Layout: The Customer Name should be printed for this element called 'Customer' when printing sales order, invoice or estimate.