src/Entity/FileEntity.php
public function getContent()
    {
        if ($this->file instanceof \Doctrine\MongoDB\GridFSFile) {
            return $this->file->getMongoGridFSFile()->getBytes();
        }
        return null;
    }
public function getContent()
    {
        if ($this->file instanceof \Doctrine\MongoDB\GridFSFile) {
            return $this->file->getMongoGridFSFile()->getBytes();
        }
        return null;
    }
Returns the binary data of a file

@see \Core\Entity\FileInterface::getContent()
@return null|string