diff --git a/commerce_invoice.api.php b/commerce_invoice.api.php
new file mode 100644
index 0000000..11daf8e
--- /dev/null
+++ b/commerce_invoice.api.php
@@ -0,0 +1,27 @@
+<?php
+
+/**
+ * @file
+ * Hooks and documentation related to paragraphs module.
+ */
+
+/**
+ * @addtogroup hooks
+ * @{
+ */
+
+/**
+ * Alter the filename that is used for the generated invoice file.
+ *
+ * Note: Don't add a file ending (".pdf").
+ *
+ * @param $file_name
+ * @param \Drupal\commerce_invoice\Entity\InvoiceInterface $
+ */
+function hook_commerce_invoice_filename_alter(&$file_name, \Drupal\commerce_invoice\Entity\InvoiceInterface $invoice) {
+  $file_name = $invoice->id() . '-invoice';
+}
+
+/**
+ * @} End of "addtogroup hooks".
+ */
diff --git a/commerce_invoice.install b/commerce_invoice.install
index 34949dc..9221c45 100644
--- a/commerce_invoice.install
+++ b/commerce_invoice.install
@@ -5,6 +5,7 @@
  * Contains install and update functions for Commerce Invoice.
  */
 
+use Drupal\Core\Field\BaseFieldDefinition;
 use Drupal\Core\StreamWrapper\PrivateStream;
 
 /**
@@ -34,3 +35,18 @@ function commerce_invoice_update_8200() {
   $field_definition->setTranslatable(FALSE);
   $definition_update_manager->updateFieldStorageDefinition($field_definition);
 }
+
+/**
+ * Add a new reference field to invoice entity for the generated invoice file.
+ */
+function commerce_invoice_update_8201() {
+  $definition_manager = \Drupal::entityDefinitionUpdateManager();
+  // Create a new field definition.
+  $new_file_field = BaseFieldDefinition::create('entity_reference')
+    ->setLabel(t('Invoice PDF'))
+    ->setSetting('target_type', 'file')
+    ->setDescription(t('The generated pdf file of the invoice.'))
+    ->setDisplayConfigurable('view', TRUE);
+  // Install the new definition.
+  $definition_manager->installFieldStorageDefinition('invoice_file', 'commerce_invoice', 'commerce_invoice', $new_file_field);
+}
diff --git a/src/Entity/Invoice.php b/src/Entity/Invoice.php
index 374b9e4..71da021 100644
--- a/src/Entity/Invoice.php
+++ b/src/Entity/Invoice.php
@@ -781,6 +781,12 @@ class Invoice extends CommerceContentEntityBase implements InvoiceInterface {
       ])
       ->setDisplayConfigurable('view', TRUE);
 
+    $fields['invoice_file'] = BaseFieldDefinition::create('entity_reference')
+      ->setLabel(t('Invoice PDF'))
+      ->setDescription(t('The generated pdf file of the invoice.'))
+      ->setSetting('target_type', 'file')
+      ->setDisplayConfigurable('view', TRUE);
+
     return $fields;
   }
 
diff --git a/src/InvoicePrintBuilder.php b/src/InvoicePrintBuilder.php
index 74c9710..aa55939 100644
--- a/src/InvoicePrintBuilder.php
+++ b/src/InvoicePrintBuilder.php
@@ -76,23 +76,19 @@ class InvoicePrintBuilder implements InvoicePrintBuilderInterface {
    * {@inheritdoc}
    */
   public function savePrintable(InvoiceInterface $invoice, PrintEngineInterface $print_engine, $scheme = 'private') {
-    $filename = $this->generateFilename($invoice);
     $langcode = $invoice->language()->getId();
-    $files = $this->fileStorage->loadByProperties([
-      'uri' => "$scheme://$filename",
-      'langcode' => $langcode,
-    ]);
-
-    if ($files) {
-      return $this->fileStorage->load(key($files));
+    // If an invoice file already exists, return existing object.
+    if (!$invoice->invoice_file->isEmpty()) {
+      //return $invoice->invoice_file->entity;
     }
+    // Create a file based in the current invoice.
     $config = $this->configFactory->get('entity_print.settings');
+    $filename = $this->generateFilename($invoice);
     $uri = $this->printBuilder->savePrintable([$invoice], $print_engine, $scheme, $filename, $config->get('default_css'));
-
     if (!$uri) {
       return FALSE;
     }
-
+    // Create a permanent file object.
     $file = $this->fileStorage->create([
       'uri' => $uri,
       'uid' => $this->currentUser->id(),
@@ -100,6 +96,9 @@ class InvoicePrintBuilder implements InvoicePrintBuilderInterface {
       'status' => FILE_STATUS_PERMANENT,
     ]);
     $file->save();
+    // Update the reference in the invoice.
+    $invoice->invoice_file = $file;
+    $invoice->save();
     return $file;
   }
 
@@ -113,9 +112,10 @@ class InvoicePrintBuilder implements InvoicePrintBuilderInterface {
    *   The generated filename.
    */
   protected function generateFilename(InvoiceInterface $invoice) {
-    $file_name = $this->filenameGenerator->generateFilename([$invoice]);
-    $file_name .= '-' . $invoice->language()->getId() . '-' . str_replace('_', '', $invoice->getState()->getId()) . '.pdf';
-    return $file_name;
+    $base_file_name = $this->filenameGenerator->generateFilename([$invoice]);
+    $file_name = $base_file_name . '-' . $invoice->language()->getId() . '-' . str_replace('_', '', $invoice->getState()->getId()) . '.pdf';
+    \Drupal::moduleHandler()->invokeAll('commerce_invoice_filename_alter', [&$file_name, $invoice]);
+    return $file_name . '.pdf';
   }
 
 }