Seller details on the PDF invoice in PrestaShop

The easiest way is to edit the file 'pdf/invoice.addresses-tab.tpl'.

Find and replace:

<td width="50%">{if $delivery_address}<span class="bold">{l s='Delivery address' d='Shop.Pdf' pdf='true'}</span><br/><br/>
       {$delivery_address}
    {/if}
</etc.>

on

 <td width="50%" >
            <br/><br/>
            <span class="bold">Seller details</span>
            <br/>
            <br/>
            company name <br/>
            company name cont. <br/>
            street <br/>
            postal code and city
            <br />
            {if isset($shop_details)}
                {$shop_details|escape:'html':'UTF-8'}<br />
            {/if}
</etc.>

The downside to this solution is that when you update PrestaShop, the original state will be restored. However, I think it's cheaper than developing a module, overwriting it, or buying an expensive module that does the same thing.

So I'm posting this advice as a temporary solution.