/**
 * @var MagentoFrameworkFilesystemDirectoryReadInterface
 */
protected $_rootDirectory;

/**
 * AddFontToPdf constructor.
 * @param MagentoFrameworkFilesystem $filesystem
 */
public function __construct(
    MagentoFrameworkFilesystem $filesystem
)
{
    $this->_rootDirectory = $filesystem->getDirectoryRead(DirectoryList::ROOT);
}

public function beforeDrawLineBlocks($subject, $page, array $draw, array $pageSettings = [])
{
    foreach ($draw as $key => $values) {
        if(isset($values['lines'])) {
            $lines = $values['lines'];
            foreach ($lines as $k => $v) {
                foreach ($v as $k1 => $v1) {
                    $v[$k1]['font_file'] = $this->_rootDirectory->getAbsolutePath('lib/internal/DejaVu/DejaVuSansCondensed.ttf');
                    $lines[$k][$k1] = $v[$k1];
                }
            }

            $draw[$key]['lines'] = $lines;
        }

    }
    // Update the $draw array to add your font
    return [$page, $draw, $pageSettings];
}