Why does elasticsearch only search in one field?

Question

PHP

Good day everyone.
I don’t understand a little here why elasticsearch searches for only one field, namely title.
Here is the indexing (I index the .docx file using ingest-attachment):

$fullfile = __DIR__.'/prrr23.docx';
      $params = [
          'index' => 'factoryfiles',
          'type'  => 'files',
          'id'    => 'testId',
          'pipeline' => 'filesNtd',
          'body'  => [
              'contentdocs' => base64_encode(file_get_contents($fullfile)),
              'title' => 'Заголовок тестового документа',
          ],
      ];


      $x = $this->obj->index($params);

And here is the search

$query = [
        'multi_match' => [
            'query' => '*жирным*',
            'fields' => ['title', 'contentdocs'],
        ],
    ];
        $searchParams = [
          'index' => 'factoryfiles',
          'type' => 'files',
          'body' => [
              'query' => $query
            ],
      ];
      $x = $this->obj->search($searchParams);

Those. if the search word in the query field is in the title at the index, then everything is displayed without problems, but if in the text of the document itself and goes to the contentdocs field, then the search does not occur
Please tell me what I'm doing wrong
Thank you in advance and everyone on Friday)