Is there a way we can add custom attachments in the email template?

Summary:

Requirement: Add a custom attachment file in the email notification.

NOTE: The attachment contains a section where we must retrieve a value from a field; other values like dates will change dynamically.

Current configuration: Object workflow is used to trigger email notifications. The custom object will determine the attachment's details, while the standard object—Activity—is where the object workflow is.

Flow: An activity record will be created whenever a record is created in the custom object. An email notification will be sent as soon as the activity is created.

Other details: We have already attempted to include a docx file in the email template's Attachments section, but it appears that field mapping isn't working.