Hi,
To make customization you need to inherit the current "external_layout_din5008" template and add the VAT information inside the information div
example:
<template id="inherit_external_layout_din5008"
inherit_id="l10n_din5008.external_layout_din5008">
<xpath expr="//div[hasclass('information_block')]"
position="replace">
<div class="information_block"
style="margin-bottom: -5mm; margin-left: 5mm;">
<t t-if="'l10n_din5008_template_data' in company"
t-set="template_data"
t-value="company.l10n_din5008_template_data"/>
<t t-if="o and 'l10n_din5008_template_data' in o"
t-set="template_data"
t-value="o.l10n_din5008_template_data"/>
<table>
<t t-foreach="template_data"
t-as="row">
<tr>
<td>
<t t-out="row[0]"/>
</td>
<td>
<t t-out="row[1]"/>
</td>
</tr>
</t>
<t t-if="delivery_det">
<tr t-if="delivery_det.origin">
<td t-if="delivery_det.origin"
name="div_origin">
<strong>Order:</strong>
</td>
<td>
<span t-field="delivery_det.origin"/>
</td>
</tr>
<tr name="div_sched_date">
<td t-if="o.state"
class="col-auto"
name="div_sched_date">
<strong>Shipping Date:
</strong>
</td>
<td>
<span t-if="delivery_det.state == 'done'"
t-esc="delivery_det.date_done.date().strftime('%d/%m/%Y')"/>
<span t-else=""
t-esc="delivery_det.scheduled_date.date().strftime('%d/%m/%Y')"/>
</td>
</tr>
<tr t-if="delivery_det.sale_id.user_id">
<td>
<strong>Sales Person
</strong>
</td>
<td>
<span t-esc="http://delivery_det.sale_id.user_id.name" target="_blank">delivery_det.sale_id.user_id.name"/>
</td>
</tr>
</t>
<tr t-if="company.vat">
<td >
VAT No.
</td>
<td>
<t t-out="company.vat"/>
</td>
</tr>
<tr t-if="payment_term">
<td>
Payment Terms
</td>
<td>
<t t-esc='payment_term'/>
</td>
</tr>
</table>
</div>
</xpath>
</template>
The above is just an example of inheriting the layout template and replacing the information block div to add the company VAT inside it.
--
Hope it helps