How to use the docxtpl.Document function in docxtpl

def include_docx_template(template_file, **kwargs):
    """Include the contents of one docx file inside another docx file."""
    if this_thread.evaluation_context is None:
        return 'ERROR: not in a docx file'
    if template_file.__class__.__name__ in ('DAFile', 'DAFileList', 'DAFileCollection', 'DALocalFile'):
        template_path = template_file.path()
    else:
        template_path = package_template_filename(template_file, package=this_thread.current_package)
    sd = this_thread.misc['docx_template'].new_subdoc()
    sd.subdocx = Document(template_path)

    # We need to keep a copy of the subdocs so we can fix up the master template in the end (in parse.py)
    # Given we're half way through processing the template, we can't fix the master template here
    # we have to do it in post
    if 'docx_subdocs' not in this_thread.misc:
        this_thread.misc['docx_subdocs'] = []
    this_thread.misc['docx_subdocs'].append(deepcopy(sd.subdocx))

    # Fix the subdocs before they are included in the template
    fix_subdoc(this_thread.misc['docx_template'], sd.subdocx)

    first_paragraph = sd.subdocx.paragraphs[0]
    for key, val in kwargs.items():
        if hasattr(val, 'instanceName'):
            the_repr = val.instanceName
        else: