By selecting "Print templates" tab in print settings, you have the option to choose preferred font for all A4 templates, including invoice and reports.
Invoice settings
Below options applies to invoice, proforma invoice and refund templates.
Title
You can change invoice title by entering any value you wish to be printed. If left empty, default invoice title is used.
Print in A5 size
When enabled, invoice will print in A5 size.
Columns selection
Select if you wish to print tax and discount columns in your invoice.
Customer details
Similar to customizing receipt, you can choose what customer details are printed in invoice. Customer name and address are always printed.
Other settings
Here you have the ability to enter a default footer for your invoice. For example, you can use it as a "thank you" note or to enter your Terms & Conditions.