Edit your invoices in Prestashop 1.7 via a Custom Module & Admin Controller

modules-my_module-controllers-admin-AdminCustomInvoicesController.php

<?php

class AdminCustomInvoicesController extends ModuleAdminController {
  public function __construct(){
    parent::__construct();
    $this->bootstrap = true; // use Bootstrap CSS
    $this->table = 'order_invoice'; // SQL table name, will be prefixed with _DB_PREFIX_
    $this->identifier = 'id_order_invoice'; // SQL column to be used as primary key
    $this->className = 'OrderInvoice'; // PHP class name
    $this->allow_export = true; // allow export in CSV, XLS..
    $this->_orderBy = 'date_add'; // default SQL ORDER BY
    $this->page_header_toolbar_title = 'Invoices'; // toolbar title
    $this->_select = 'concat(upper(c.lastname), " ", c.firstname) as customer';
    $this->_join = '
      JOIN '._DB_PREFIX_.'orders o ON (o.id_order = a.id_order)
      JOIN '._DB_PREFIX_.'customer c ON (c.id_customer = o.id_customer)
    ';

    $this->fields_list = [
      'id_order_invoice' => ['title' => $this->trans('ID', [], 'Admin.Global'),'class' => 'fixed-width-xs'],
      'number' => ['title' => $this->trans('Number', [], 'Admin.Global'),'class' => 'fixed-width-xs'],
      'date_add' => ['title' => $this->trans('Date', [], 'Admin.Global'), 'type'=>'datetime'],
      'customer' => ['title' => $this->trans('Customer', [], 'Admin.Global')],
      'total_products_wt' => ['title' => $this->trans('Total products', [], 'Admin.Global'),
        'align' => 'text-right',
        'type' => 'price',
      ],
      'total_shipping_tax_incl' => ['title' => $this->trans('Total shipping', [], 'Admin.Global'),
        'align' => 'text-right',
        'type' => 'price',
      ],
      'total_paid_tax_incl' => ['title' => $this->trans('Total paid', [], 'Admin.Global'),
        'align' => 'text-right',
        'type' => 'price',
      ],
    ];

    $this->addRowAction('edit');
    $this->addRowAction('details');

    $this->fields_form = [
      'legend' => ['title' => $this->l('Custom Invoice'),'icon' => 'icon-list-ul'],
      'input' => [
        ['name' => 'date_add','type' => 'datetime','label' => 'Date add',],
        ['name'=>'number','type'=>'text','required' => true,'label' => 'Number',],
        ['name'=>'note','type'=>'textarea','label' => 'Note',],
        ['name'=>'delivery_number','type'=>'text','label'=>'Delivery number'],
        ['name'=>'delivery_date','type'=>'datetime','label'=>'Delivery date'],
        ['name'=>'total_discount_tax_excl','type'=>'text','label'=>'Total amount of discounts (no tax)'],
        ['name'=>'total_discount_tax_incl','type'=>'text','label'=>'Total amount of discounts (with tax)'],
        ['name'=>'total_shipping_tax_excl','type'=>'text','label'=>'Total cost of shipping (no tax)'],
        ['name'=>'total_shipping_tax_incl','type'=>'text','label'=>'Total cost of shipping (with tax)'],
        ['name'=>'total_products','type'=>'text','label'=>'Total cost of products (no tax)'],
        ['name'=>'total_products_wt','type'=>'text','label'=>'Total cost of products (with tax)'],
        ['name'=>'total_wrapping_tax_excl','type'=>'text','label'=>'Total cost of wrapping (no tax)'],
        ['name'=>'total_wrapping_tax_incl','type'=>'text','label'=>'Total cost of wrapping (with tax)'],
        ['name'=>'total_paid_tax_excl','type'=>'text','label'=>'Total paid (no tax)'],
        ['name'=>'total_paid_tax_incl','type'=>'text','label'=>'Total paid (with tax)'],
        ['name'=>'shop_address','type'=>'textarea','label'=>'Shop address'],
      ],
      'submit' => ['title' => $this->trans('Save', [], 'Admin.Actions'),]
    ];

    $this->addRowAction('delete');
    $this->bulk_actions = [
      'delete' => [
        'text' => 'Delete',
        'icon' => 'icon-power-off'
      ],
    ];
  }

  public function renderForm(){
    $invoice = $this->object; // get invoice
    $order = $invoice->getOrder(); // get order
    $customer = $order->getCustomer(); // get customer
    $currency = new Currency($order->id_currency); // get currency
    // add some info in an HTML string
    $info = '<div class="panel">';
    $info .= '<div class="panel-heading"><i class="icon-list-ul"></i> Order informations</div>';
    $info .= "Order reference: {$order->reference}<br/>";
    $info .= "Customer: {$customer->firstname} {$customer->lastname}<br/>";
    $info .= "Total_paid : ".Tools::displayPrice($order->total_paid, $currency)."<br/>";
    $info .= "Get total paid : ".Tools::displayPrice($order->getTotalPaid(), $currency)."<br/>";
    $info .= "Payment: {$order->payment}<br/>";
    $info .= "Order state : {$order->getCurrentOrderState()->name[$this->context->language->id]}";
    $info .= '</div>';
    // push the HTML to $this->content
    $this->content .= $info;
    return parent::renderForm();
  }

  public function access($action, $disable = false){
    return true;
  }
}

modules-my_module-my_module.php

<?php
if (!defined('_PS_VERSION_')) {exit;}
class My_Module extends Module {
      public function __construct() {
      $this->name = 'my_module';
      $this->tab = 'administration';
      $this->version = '1.0.0';
      $this->author = 'Florian Courgey';
      $this->bootstrap = true;
      parent::__construct();
      $this->displayName = $this->l('PrestaShop Module by FC');
      $this->description = $this->l('Improve your store by [...]');
      $this->ps_versions_compliancy = ['min' => '1.7', 'max' => _PS_VERSION_];
  }
}

Full tutorial available at https://floriancourgey.com/2018/04/edit-your-invoices-in-prestashop/?ref=github