Hi,

You may try like this in your module.

Create a file custom_saleorder.xml under views folder in your module. Also mention it in __openerp__.py file.

Then add following code in the file, to have customer reference in sale order:

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="report_saleorder_inherited" inherit_id="sale.report_saleorder_document">
            
            <xpath expr="//t/div/div[3]/div[1]" position="after">
                <div t-if="o.partner_id.ref" class="col-xs-3">
                    <strong>Customer Reference:</strong>
                    <p t-field="o.partner_id.ref"/>
                </div>
            </xpath>
            
       </template>
    </data>
</openerp>

Restart the server and upgrade your module. Then try.

Similarly you can override the invoice report by inheriting the corresponding invoice template.

For eg: create a file custom_invoice_report.xml file under views folder in your module. And add the following code:

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="report_invoice_document_inherited" inherit_id="account.report_invoice_document">
            
            <xpath expr="/t/div/div[2]/div[5]" position="after">
                <div t-if="o.partner_id.ref" class="col-xs-3">
                    <strong>Customer Reference:</strong>
                    <p t-field="o.partner_id.ref"/>
                </div>
            </xpath>
            
       </template>
    </data>
</openerp>

Also don't forget to mention sale, account as depends in your __openerp__.py file.