How to add attachments in Zoho Invoice mail using create zoho incoice function

How to add attachments in Zoho Invoice mail using create zoho incoice function

Dear All,

With the usage of create zoho invoice I can send an Invoice (as an email) to a user-client with a default text (which is editable through Zoho invoices.). Does anyone know (if there is any way) how can I add an attachment in  zoho.invoice.createinvoice ?
Because I would like to send an email with an attachment (which I uploaded it in a File upload button). 
I found this but I do not know how is working.