Hello,

The file is located in the addons directory account/report/invoice.rml The best solution will be to create an addon that override you current report. You can do it in XML `

<report
    auto="False"
    id="account.account_invoices"
    model="account.invoice"
    name="account.invoice"
    rml="my_addons/report/invoice.rml"
    string="Invoices"
    attachment="(object.state in ('open','paid')) and ('INV'+(object.number or '').replace('/',''))"
    attachment_use="1"/>

` By just replacing the rml attribute to your file path.

Else you can try c2c_webkit_report to have HTML based report, they may be easier to customize as you do not have to know RML.

Hello,

You will find it at this location addons/account/report/invoice.rml. you can edit it according to your need.

Secondly you can open the invoice report using report designer plugin.

To check the path of the rml used go to Settings/Customization/Low Level Objects/Actions/Reports. search for object account.invoice and edit the entry in form view . It may be possible that you want be able to see changes applied on rml due to the argument reload from attachment. If this is True then the report will be printed from the attachments. So to see the changes you need to either set this argument to False or delete the attachment and then print the report.