muk_web/muk_web_preview_attachment/static/src/xml/widget_preview.xml

<?xml version="1.0" encoding="UTF-8"?>

<!--     
	Copyright (C) 2017 MuK IT GmbH
	
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as
    published by the Free Software Foundation, either version 3 of the
    License, or (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>. 
-->

<templates>
	<t t-extend="FieldBinaryFileUploader.files">
		<t t-jquery="a[target='_blank']" t-operation="before">
			<t t-if="widget.mode === 'readonly'">
				<button type="button" class="o_attachment_preview" aria-hidden="true" t-att-data-id="file.data.id">
					<i class="fa fa-file-text-o" t-att-data-id="file.data.id"></i>
				</button>
			</t>
		</t>
		<t t-jquery=".o_image" t-operation="attributes">
			<attribute name="t-att-data-id">widget.metadata[file.id] ? file.data.id : false</attribute>
		</t>
	</t>
</templates>