You can add attachments alongside your invoices or estimates when sending them by email. To add an attachment, click on Choose file... in the email sending window. All major file types are supported (e.g. pdf, zip, jpg etc.) and the maximum size of all attached files that can be sent in a single email is 20MB. Please note, that this feature is a Premium Service, and as such you need a Premium subscription to use it. The invoice or estimate is always automatically added as an attachment.