There are a few ways to print invoices. When you generate your invoices, you are given the option to print them afterwards.
Or you can print them from the invoice page.
Or you can print them from the reports page.
As an example, let's print them from the invoice page.
Make sure you are on the invoice page. You can highlight multiple invoices at once by either holding down the ctrl key and clicking on them or hold the shift key down and click on the first and last invoice you want to highlight.
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The invoices highlighted in blue are the ones which will be printed when you click on the print button. You can unhighlight certain invoices by holding down the ctrl key and clicking on the invoices you don't want printed.