If you want to override the default invoice template by your custom module, with different header and footer, refer the following code:
<openerp>
<data>
<template id="report_invoice_document_inherited" inherit_id="account.report_invoice_document">
<xpath expr="//t[@t-call='report.external_layout']" position="replace">
<t t-call="report.new_layout">
<div class="page">
<t t-set="company" t-value="res_company">
</t>
<br />
<div class="row mt16 mb16">
<div class="col-xs-5">
<br />
<div style="background:#01008A; font-size:13.5pt;font-family:"Helvetica",sans-serif;color:white" valign="top">
<strong><center>Bill To</center></strong>
</div>
<address style="padding:5px 5px 5px 5px;border-width: 1px; border-style: solid; border-color: #002b49;" t-field="o.address_shipping_id" t-field-options="{"widget": "contact", "fields": ["address", "name"], "no_marker": true}"/>
</div>
<div class="col-xs-5 col-xs-push-2" >
<br />
<div style="background:#01008A; font-size:13.5pt;font-family:"Helvetica",sans-serif;color:white" valign="top">
<strong><center>Ship To</center></strong>
</div>
<address style="padding:5px 5px 5px 5px;border-width: 1px; border-style: solid; border-color: #002b49;" t-field="o.partner_id" t-field-options="{"widget": "contact", "fields": ["address", "name"], "no_marker": true}"/>
</div>
</div>
<h2>
<span t-if="o.type == 'out_invoice' and (o.state == 'open' or o.state == 'paid')">Invoice</span>
<span t-if="o.type == 'out_invoice' and o.state == 'proforma2'">PRO-FORMA</span>
<span t-if="o.type == 'out_invoice' and o.state == 'draft'">Draft Invoice</span>
<span t-if="o.type == 'out_invoice' and o.state == 'cancel'">Cancelled Invoice</span>
<span t-if="o.type == 'out_refund'">Refund</span>
<span t-if="o.type == 'in_refund'">Supplier Refund</span>
<span t-if="o.type == 'in_invoice'">Supplier Invoice</span>
<span t-field="o.number"/>
</h2>
<div class="row mt32 mb32">
<div class="col-xs-2" t-if="o.name">
<strong>Description:</strong>
<p t-field="o.name"/>
</div>
<div class="col-xs-2" t-if="o.date_invoice">
<strong>Invoice Date:</strong>
<p t-field="o.date_invoice"/>
</div>
<div class="col-xs-2" t-if="o.origin">
<strong>Source:</strong>
<p t-field="o.origin"/>
</div>
<div class="col-xs-2" t-if="o.partner_id.ref">
<strong>Customer Code:</strong>
<p t-field="o.partner_id.ref"/>
</div>
<div class="col-xs-2" t-if="o.reference">
<strong>Reference:</strong>
<p t-field="o.reference"/>
</div>
</div>
<div class="row mt16 mb16">
<div class="col-xs-12">
<table class="table table-condensed" style="border-left:1px solid #000000;border-top:1px solid #000000;border-right:1px solid #000000;">
<thead>
<tr style="background-color:#F4F4F4;">
<th style="border:1px solid #000000;">Quantity</th>
<th style="border:1px solid #000000;">Item Code</th>
<th style="border:1px solid #000000;">Description</th>
<th class="text-right" style="border:1px solid #000000;">Price Each</th>
<th class="text-right" style="border:1px solid #000000;">Amount</th>
</tr>
</thead>
<tbody class="invoice_tbody">
<t t-set="item_no" t-value="1" />
<tr style="border:1px solid #000000;" t-foreach="o.invoice_line" t-as="l">
<t t-if="item_no%2!=0">
<td style="border-left:1px solid #000000;">
<span t-field="l.quantity"/>
</td>
<td style="border-left:1px solid #000000;">
<span t-field="l.product_id.name"/>
</td>
<td style="border-left:1px solid #000000;">
<span t-field="l.name"/>
</td>
<td style="border-left:1px solid #000000;" class="text-right">
<span t-field="l.price_unit"/>
</td>
<td style="border-left:1px solid #000000;" class="text-right">
<span t-field="l.price_subtotal" t-field-options='{"widget": "monetary", "display_currency":
"o.currency_id"}'/>
</td>
</t>
<t t-if="item_no%2==0">
<td style="border-left:1px solid #000000;background-color:#F4F4F4;">
<span t-field="l.quantity"/>
</td>
<td style="border-left:1px solid #000000;background-color:#F4F4F4;">
<span t-field="l.product_id.name"/>
</td>
<td style="border-left:1px solid #000000;background-color:#F4F4F4;">
<span t-field="l.name"/>
</td>
<td style="border-left:1px solid #000000;background-color:#F4F4F4;" class="text-right">
<span t-field="l.price_unit"/>
</td>
<td style="border-left:1px solid #000000;background-color:#F4F4F4;" class="text-right">
<span t-field="l.price_subtotal" t-field-options='{"widget": "monetary", "display_currency":
"o.currency_id"}'/>
</td>
</t>
<t t-set="item_no" t-value="item_no+1" />
</tr>
<tr style="border-top:1px solid #000000;">
<td style="border-left:2px solid #ffffff;border-top:1px solid #000000;"></td>
<td style="border-top:1px solid #000000;"></td>
<td style="border-top:1px solid #000000;"></td>
<td style="border-left:1px solid #000000;border-bottom:1px solid #000000;border-top:1px solid #000000;"><strong>Total:</strong></td>
<td style="border-bottom:1px solid #000000;border-top:1px solid #000000;"><span t-field="o.amount_total" t-field-options='{"widget": "monetary", "display_currency":
"o.currency_id"}'/></td>
</tr>
</tbody>
</table>
</div>
</div>
<p t-if="o.comment">
<span t-field="o.comment"/>
</p>
<p t-if="o.fiscal_position.note">
<strong>Fiscal Position Remark:</strong>
<span t-field="o.fiscal_position.note"/>
</p>
</div>
</t>
</xpath>
</template>
<template id="report.new_layout">
<!-- Multicompany -->
<t t-if="o and 'company_id' in o">
<t t-set="company" t-value="o.company_id"></t>
</t>
<t t-if="not o or not 'company_id' in o">
<t t-set="company" t-value="res_company"></t>
</t>
<t t-call="report.new_layout_header" />
<t t-raw="0" />
<t t-call="report.new_layout_footer" />
</template>
<template id="report.new_layout_header">
<div class="header">
<div class="row">
<div class="col-xs-3">
<img t-if="company.logo" t-att-src="'data:image/png;base64,%s' % company.logo" style="max-height: 45px;"/>
</div>
<div class="col-xs-9 text-right" style="margin-top:20px;" t-field="company.rml_header1"/>
</div>
<div class="row zero_min_height">
<div class="col-xs-12">
<div style="border-bottom: 1px solid black;"></div>
</div>
</div>
<div class="row mt8 mb8">
<div class="col-xs-5">
<div t-field="company.partner_id"
t-field-options='{"widget": "contact", "fields": ["address", "name"], "no_marker": true}'
style="border:1px solid #000000;"/>
</div>
</div>
</div>
</template>
<template id="report.new_layout_footer">
<div class="footer">
<div t-if="company.sale_note" class="row mt16 mb16">
<div class="col-xs-6">
<div style="border:1px solid #000000;background-color:#01008A;color:#ffffff">
<strong>International Banking Detail</strong>
</div>
<div style="border:1px solid #000000;">
<div t-field="company.sale_note"/>
</div>
</div>
</div>
</div>
</template>
</data>
</openerp>
You want to override the default invoice template by your custom module?