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 (Settings > Billing & Invoices > Template Assignments) or project level (Projects > General > Billing Options).
To print invoices in a batch:
In the Invoices screen, select all the invoices on the grid that you want to print.
Click Actions > Preview. CORE groups the invoice preview by the template being used.
Click the Print icon on the viewer (browser window/tab). Check Viewer for more on this.