Even though I don't use this feature, you can add attachments to a Customer Invoice.After the new invoice has been saved click the Invoice transaction in the register to highlight it.Look for a grey paperclip icon in the transaction line and click it to add your attachment.
Do retain your paper documents, though. As it stands right now, the attachments feature is not yet an industrial strength application and there is a chance that attachments can get lost in the shuffle.
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