let us check what i made wrong
i went to menu "display" and then to "views"
i looked for my backend (=isis) in the view "order" and find the file "invoice"
in this file i edit one row for the logo. example:
<table style="width: 100%;">
<tbody>
<tr>
<td><img src="images/logotierschutzfutter.jpg" alt="logotierschutzfutter" style="float: left;" /></td>
</tr>
<tr>
<td>
<h1 style="text-align: center;"> </h1>
<br /> </td>
</tr>
<tr>
<td>
<div style="float: right; width: 100px; padding-top: 20px;"> </div>
<p> </p>
</td>
</tr>
<tr>
<td><br /> <br />
<table style="width: 100%;">
<tbody>
<tr>
<td> </td>
<td> </td>
</tr>
</tbody>
</table>
but it will not show on the frontend.