Solution
The form archive is a file type process data. You can add it as a file attachment to a custom notification email template by using the following macro:
<WF_PROCESS_INST_RELDATA_FILE.FORM_ARCHIVE>
This macro will be automatically detected and replaced with a file attachment containing the form archive when sending email notifications.
The above post is missing the macro. Can you correct it.
You can use macro: <WF_PROCESS_INST_RELDATA_VALUE.YOUR_FILE_PROCESS_DATA_NAME> to attach the actual file type process data in your custom email as attachment (not a link)
Hence you can have the form archive html file as attachment if you add this tag:
<WF_PROCESS_INST_RELDATA_VALUE.FORM_ARCHIVE> at the bottom of your email template file.