OpenERP is quite powerful in terms of internationalization of reports. So in most cases there should be a way to use the existing features for what you want to achieve. Also there is the comments field which can be used to write additional text to the invoice.

If this is still not enough for your case, you have got two options: - use a pdf edit tool to edit the pdf reports generated by OpenERPs reporting system - switch to another reporting engine like Aeroo Reports (https://launchpad.net/aeroo), with allows to generate reports in a variety of formats like odt, doc, xls, and so on. Unfortunately this switch also includes rewriting all the reports you wish to edit.