nopCommerce 4.00 allow to get button without any modification. Just proceed to Orders list and click button.
For older nopCommerce versions you need to proceed as below.
At the configuration plugin page, click Install String Resources.
Next, go to Administration → Content Management → Widgets → PDF Invoice and set active.
If you want to show extra button on the page Order List, you need to modify file
And add line at the bottom of the file @Html.Widget("PdfPluginOrderList")
The final result will be like:
If you want to show extra button on the page Order Edit, you need to modify file
And add line @Html.Widget("PdfPluginOrderEdit", Model.Id)
just before line with: @Html.DeleteConfirmation("order-delete")
And the final result:
The last thing is to set setting on true:
Go to Settings/All Settings (Advanced) and find setting named htmlpdfsettings.createtemporarypackingslip
Change value to true.