How to get a file path of the node?

For my Drupal 8 website I need to implement a PDF downloader. I have created a content type; which has a “File upload” fields. I have created a view, where all the titles of the nodes are displayed. In combination of “Views Bulk Operations” module and external php library I have created a new Action. After the user cheched the nodes, which he would like to download, the action should be initialized. My question is, how can I get the path to the file in the execute() function?

/** * {@inheritdoc} */ public function execute($  entity = NULL) {  // Do some processing.. /* $  node = Node::load(nid); $  file_path = drupal_realpath($  node->field_pdf_file->entity->getFileUri()); $  file_name = $  node->field_pdf_file->entity->getFilename(); */ // Access nodes pdf field  // Merge them  $  merger->addFile($  file_name);  $  createdPdf = $  merger->merge();  return $  this->t('Some result'); }