Zoho Invoice lets you attach files upto 10MB with your invoice notification emails. To do this:​

• Click the Invoices tab. Select the invoice you wish to send from the Invoices page.
• Now, click the down arrow near the cog wheel of the invoice you selected, and then click Email Invoice. Or you can also reach this page by clicking the invoice you want, and then from the Invoice Details section, click Email Invoice.
• The notification email to be sent appears on the Send Invoice page.
• Click the Attach a file link to attach the file.
• Once you are done attaching the file, click the Send button.

Note: You can attach any number of files. To remove a file, click the red X symbol adjacent to it.