Core allows you to preview and print invoices in a batch for the purpose of bulk printing. You can set the default invoice template at the global level (Global Settings > Template Assignments) or project level (Projects > General > Billing Options). 

To print invoices in a batch:

1. In the Invoices screen, select all the invoices on the grid that you want to print.
2. Click Actions > Preview. Core groups the invoice preview by the template being used.
3. Click the Print icon on the viewer (browser window/tab). Check the Core Help for details.

Check Viewer for more on this.