Yes, you can produce proforma invoices in Unleashed. You create an Invoice template that shows the title Proforma Invoice, then use it on the invoices you need. Classic and Formal templates can't be edited, so you'll need to create an editable copy first.
Create the template
From the main menu, click Settings, then click Doc Designer.
Click Invoices.
In the Document tab, use the Template Name drop-down menu to select the template you want to edit.
In the template layout, select the invoice type field that prints the document title, then delete it using the Component tab.
Click the Toolbox tab, then drag the Text component to where you want the title to appear.
Click the new label, then click the Component tab.
Enter Proforma Invoice as the text, then format it as you need.
Click Save Now, then click Publish.
Use the template on an invoice
You can use your proforma template in two ways:
Change the template on an invoice that already exists.
Set it as a customer's default invoice template so their new invoices use it.