diff --git a/src/Component/Utility/FillPdf.php b/src/Component/Utility/FillPdf.php
index f04fdc36a6b192a92f1f52317a712550a8de197d..bb5bbc530f4413d5b2d56ad457812f8601910e90 100644
--- a/src/Component/Utility/FillPdf.php
+++ b/src/Component/Utility/FillPdf.php
@@ -28,7 +28,7 @@ class FillPdf {
     if (empty($pdftk_path)) {
       $pdftk_path = 'pdftk';
     }
-    $process = new Process($pdftk_path . ' --version');
+    $process = new Process([$pdftk_path, '--version']);
     $process->run();
 
     // Check there's no error code and the --version output includes "pdftk".
diff --git a/src/OutputHandler.php b/src/OutputHandler.php
index a0282cf10802ead30aef92d2c496476e982bb4d2..a83e97f8a7370202f4d95b8afc346cee4dbec838 100644
--- a/src/OutputHandler.php
+++ b/src/OutputHandler.php
@@ -98,7 +98,7 @@ class OutputHandler implements OutputHandlerInterface {
     }
     else {
       // Full steam ahead!
-      $saved_file = file_save_data($configuration['data'], "{$resolved_destination_path}/{$configuration['filename']}", FileSystemInterface::EXISTS_RENAME);
+      $saved_file = \Drupal::service('file.repository')->writeData($configuration['data'], "{$resolved_destination_path}/{$configuration['filename']}", FileSystemInterface::EXISTS_RENAME);
       $this->rememberFileContext($saved_file, $configuration['context']);
     }
 
diff --git a/src/Plugin/FillPdfActionPlugin/FillPdfRedirectAction.php b/src/Plugin/FillPdfActionPlugin/FillPdfRedirectAction.php
index 0cefc707440001d671888a2536719ae03637e0f2..f8a7b1922e493f19c51bc5d77b11a0a961c1e2c7 100644
--- a/src/Plugin/FillPdfActionPlugin/FillPdfRedirectAction.php
+++ b/src/Plugin/FillPdfActionPlugin/FillPdfRedirectAction.php
@@ -31,7 +31,7 @@ class FillPdfRedirectAction extends FillPdfSaveAction {
    */
   public function execute() {
     $saved_file = $this->savePdf();
-    $url = ($saved_file !== FALSE) ? file_create_url($saved_file->getFileUri()) : Url::fromRoute('<front>')->toString();
+    $url = ($saved_file !== FALSE) ? \Drupal::service('file_url_generator')->generateAbsoluteString($saved_file->getFileUri()) : Url::fromRoute('<front>')->toString();
     return new RedirectResponse($url);
   }
 
diff --git a/src/Plugin/PdfBackend/PdftkPdfBackend.php b/src/Plugin/PdfBackend/PdftkPdfBackend.php
index 5fe89cd82bb1c8fe212fd3df9c1c38eef559b8ac..cae3f0e2159c061e266ebe5b1816f1a8762f884a 100644
--- a/src/Plugin/PdfBackend/PdftkPdfBackend.php
+++ b/src/Plugin/PdfBackend/PdftkPdfBackend.php
@@ -93,7 +93,7 @@ class PdftkPdfBackend extends PdfBackendBase implements ContainerFactoryPluginIn
    * {@inheritdoc}
    */
   public function parseStream($pdf_content) {
-    $template_file = file_save_data($pdf_content);
+    $template_file = \Drupal::service('file.repository')->writeData($pdf_content);
     return $this->parseFile($template_file);
   }
 
@@ -166,7 +166,7 @@ class PdftkPdfBackend extends PdfBackendBase implements ContainerFactoryPluginIn
    * {@inheritdoc}
    */
   public function mergeStream($pdf_content, array $field_mappings, array $context) {
-    $template_file = file_save_data($pdf_content);
+    $template_file = \Drupal::service('file.repository')->writeData($pdf_content);
     return $this->mergeFile($template_file, $field_mappings, $context);
   }
 
@@ -186,7 +186,7 @@ class PdftkPdfBackend extends PdfBackendBase implements ContainerFactoryPluginIn
     $xfdf_name = $template_uri . '.xfdf';
     $xfdf = create_xfdf(basename($xfdf_name), $fields);
     // Generate the file.
-    $xfdf_file = file_save_data($xfdf, $xfdf_name, FileSystemInterface::EXISTS_RENAME);
+    $xfdf_file = \Drupal::service('file.repository')->writeData($xfdf, $xfdf_name, FileSystemInterface::EXISTS_RENAME);
 
     // @todo Improve this approach when we turn $context into a value object.
     if (!isset($context['fid'])) {
diff --git a/tests/modules/fillpdf_test/src/Plugin/PdfBackend/TestPdfBackend.php b/tests/modules/fillpdf_test/src/Plugin/PdfBackend/TestPdfBackend.php
index 1d1d05c57106a78c6ec40568d07302bd5f6ad909..4cb40113731a3a65cd337d008666b0a9a8f7739b 100644
--- a/tests/modules/fillpdf_test/src/Plugin/PdfBackend/TestPdfBackend.php
+++ b/tests/modules/fillpdf_test/src/Plugin/PdfBackend/TestPdfBackend.php
@@ -87,7 +87,7 @@ class TestPdfBackend extends PdfBackendBase implements ContainerFactoryPluginInt
    */
   public function mergeStream($pdf_content, array $field_mappings, array $context) {
     // Not really populated, but that isn't our job.
-    $populated_pdf = file_get_contents(drupal_get_path('module', 'fillpdf_test') . '/files/fillpdf_test_v3.pdf');
+    $populated_pdf = file_get_contents(\Drupal::service('extension.list.module')->getPath('fillpdf_test') . '/files/fillpdf_test_v3.pdf');
 
     $this->state->set('fillpdf_test.last_populated_metadata', [
       'field_mapping' => $field_mappings,
diff --git a/tests/src/Functional/FillPdfFormDeleteFormTest.php b/tests/src/Functional/FillPdfFormDeleteFormTest.php
index a7cf7e555c294630e12efd484350c5465b3065e3..e9d8fccc30f9c5b6f1c21d22f1329e519d3124ff 100644
--- a/tests/src/Functional/FillPdfFormDeleteFormTest.php
+++ b/tests/src/Functional/FillPdfFormDeleteFormTest.php
@@ -19,7 +19,7 @@ class FillPdfFormDeleteFormTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  static public $modules = ['fillpdf_test'];
+  protected static $modules = ['fillpdf_test'];
 
   /**
    * {@inheritdoc}
diff --git a/tests/src/Functional/FillPdfFormDuplicateFormTest.php b/tests/src/Functional/FillPdfFormDuplicateFormTest.php
index 4fa64b7e16d628fcddd0d1c523b232831db0e5ca..d81d7394e98dd9fec09fac7638e0ecc13c3db6f9 100644
--- a/tests/src/Functional/FillPdfFormDuplicateFormTest.php
+++ b/tests/src/Functional/FillPdfFormDuplicateFormTest.php
@@ -19,7 +19,7 @@ class FillPdfFormDuplicateFormTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  static public $modules = ['fillpdf_test'];
+  protected static $modules = ['fillpdf_test'];
 
   /**
    * {@inheritdoc}
diff --git a/tests/src/Functional/FillPdfFormImportFormTest.php b/tests/src/Functional/FillPdfFormImportFormTest.php
index e3e30bbfe0792bdfe3f34f0596fc88cb820dc53d..cf6ebb5ecdb0041af93260503f26050efa744d54 100644
--- a/tests/src/Functional/FillPdfFormImportFormTest.php
+++ b/tests/src/Functional/FillPdfFormImportFormTest.php
@@ -17,7 +17,7 @@ class FillPdfFormImportFormTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  static public $modules = ['fillpdf_test'];
+  protected static $modules = ['fillpdf_test'];
 
   /**
    * {@inheritdoc}
diff --git a/tests/src/Functional/FillPdfSettingsFormTest.php b/tests/src/Functional/FillPdfSettingsFormTest.php
index 990b44faf1fc198cc6073805db7517048b3e6cb7..db222d71ae7814369ac6016b7656eed578bcd4e0 100644
--- a/tests/src/Functional/FillPdfSettingsFormTest.php
+++ b/tests/src/Functional/FillPdfSettingsFormTest.php
@@ -15,7 +15,7 @@ class FillPdfSettingsFormTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  public static $modules = ['fillpdf_test', 'file_test'];
+  protected static $modules = ['fillpdf_test', 'file_test'];
 
   use TestFillPdfTrait;
 
diff --git a/tests/src/Functional/FillPdfTestBase.php b/tests/src/Functional/FillPdfTestBase.php
index cfff89fc10844f5f003eb86d102fa143ec75032f..12f0a84a7f2f968326143374ceb1030e6759d0b1 100644
--- a/tests/src/Functional/FillPdfTestBase.php
+++ b/tests/src/Functional/FillPdfTestBase.php
@@ -33,7 +33,7 @@ abstract class FillPdfTestBase extends FileFieldTestBase {
    *
    * @see \Drupal\Tests\BrowserTestBase::installDrupal()
    */
-  public static $modules = ['image', 'fillpdf_test'];
+  protected static $modules = ['image', 'fillpdf_test'];
 
   /**
    * The FillPDF link manipulator service.
diff --git a/tests/src/Functional/LinkManipulatorTest.php b/tests/src/Functional/LinkManipulatorTest.php
index bf36b460eabe45eda4b566938e307a10656f50e8..c07cd83fcbfee6eea4c7649ded0ff85b9a951c8e 100644
--- a/tests/src/Functional/LinkManipulatorTest.php
+++ b/tests/src/Functional/LinkManipulatorTest.php
@@ -20,7 +20,7 @@ class LinkManipulatorTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  static public $modules = ['fillpdf_test'];
+  protected static $modules = ['fillpdf_test'];
 
   /**
    * {@inheritdoc}
diff --git a/tests/src/Functional/PdfPopulationTest.php b/tests/src/Functional/PdfPopulationTest.php
index 5ed13b431927955f2cd7ed734bdfdba9e4400342..c0469361bca8ac7ce3e6465a9eafa913ec426511 100644
--- a/tests/src/Functional/PdfPopulationTest.php
+++ b/tests/src/Functional/PdfPopulationTest.php
@@ -28,7 +28,7 @@ class PdfPopulationTest extends FillPdfTestBase {
    *
    * @see \Drupal\Tests\BrowserTestBase::installDrupal()
    */
-  public static $modules = ['filter', 'taxonomy'];
+  protected static $modules = ['filter', 'taxonomy'];
 
   /**
    * A test vocabulary.
diff --git a/tests/src/Functional/PdfWebformPopulationTest.php b/tests/src/Functional/PdfWebformPopulationTest.php
index 86825ee365e272eca22f250f8c1d9e615d440a05..8ad79b783f76100b7697c06fdce1c2481b5ae787 100644
--- a/tests/src/Functional/PdfWebformPopulationTest.php
+++ b/tests/src/Functional/PdfWebformPopulationTest.php
@@ -30,7 +30,7 @@ class PdfWebformPopulationTest extends FillPdfTestBase {
    *
    * @see \Drupal\Tests\BrowserTestBase::installDrupal()
    */
-  public static $modules = ['webform', 'fillpdf_webform_test'];
+  protected static $modules = ['webform', 'fillpdf_webform_test'];
 
   /**
    * A test webform submission.
diff --git a/tests/src/Functional/UninstallTest.php b/tests/src/Functional/UninstallTest.php
index 24f2cba42af16fa498469e72a869427486dc5565..70380d6b0262259c4997c2a4af571464f0bf9798 100644
--- a/tests/src/Functional/UninstallTest.php
+++ b/tests/src/Functional/UninstallTest.php
@@ -18,7 +18,7 @@ class UninstallTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  static public $modules = ['fillpdf_test'];
+  protected static $modules = ['fillpdf_test'];
 
   /**
    * {@inheritdoc}
diff --git a/tests/src/Kernel/FillPdfKernelTestBase.php b/tests/src/Kernel/FillPdfKernelTestBase.php
index 74303557c242b26f6465db81dc856dd7f5a435fc..a70dd65f6e25a799595969946cf0ea27a082238f 100644
--- a/tests/src/Kernel/FillPdfKernelTestBase.php
+++ b/tests/src/Kernel/FillPdfKernelTestBase.php
@@ -14,7 +14,7 @@ abstract class FillPdfKernelTestBase extends EntityKernelTestBase {
    *
    * @var array
    */
-  public static $modules = [
+  protected static $modules = [
     'file',
     'link',
     'token',
diff --git a/tests/src/Traits/TestFillPdfTrait.php b/tests/src/Traits/TestFillPdfTrait.php
index 3bfd4e76f6d24e8ab8ffdf1340a94415477395bc..f37909aa2fac9fac64b41dcc65337fc521c345ea 100644
--- a/tests/src/Traits/TestFillPdfTrait.php
+++ b/tests/src/Traits/TestFillPdfTrait.php
@@ -148,7 +148,7 @@ trait TestFillPdfTrait {
   protected function getTestPdfPath($filename) {
     /** @var \Drupal\Core\File\FileSystem $file_system */
     $file_system = $this->container->get('file_system');
-    return $file_system->realpath(drupal_get_path('module', 'fillpdf') . '/tests/modules/fillpdf_test/files/' . $filename);
+    return $file_system->realpath(\Drupal::service('extension.list.module')->getPath('fillpdf') . '/tests/modules/fillpdf_test/files/' . $filename);
   }
 
   /**