You can also send attachments in automated emails.
In Settings > Workflows, automate email external notification and document template to the same stage. Note: both templates need to have same label.
Setup templates (email message and attachment document)
You need to setup external notification template and also to upload the document to Merge templates that will be sent. Label them both accordingly with the same document label.
2. Assign templates to automation
After that go to Workflow settings, pick a stage where you want this to apply. Hit “Automate” button and add both of these templates. When executed External notification will contain merged document as an attachment.
Clients will get it like this (message and attachment):
NOTE: It is possible to add multiple merge documents to be sent as attachment. You will just add multiple merge document templates with external notification to the stage.