Hi Marcelo
If you can filter the grid to only show the work orders you want to invoice then you can use the 'Invoice all...' link under the 'More actions...' button. This should run across all pages of a filtered grid. Would this work for you?
If you wanted to invoice work orders that aren't in status of 'To be invoiced' you could copy the 'Invoice all...' button actions to a new button. Then you could adjust the Start Loop Through Grid so the status is different.
Jeff