How do I use another solution as reference with nuget packages

public static string PdfOku(string _link)
      {
          StringBuilder _stringBuilder = new StringBuilder();
          PdfReader _pdfReader = new PdfReader(_link);
          for (int page = 1; page <= _pdfReader.NumberOfPages; page++)
          {
              ITextExtractionStrategy strategy = new SimpleTextExtractionStrategy();
              string currentText = PdfTextExtractor.GetTextFromPage(_pdfReader, page, strategy);

              currentText = Encoding.UTF8.GetString(ASCIIEncoding.Convert(Encoding.Default, Encoding.UTF8, Encoding.Default.GetBytes(currentText)));
              _stringBuilder.Append(currentText);
              _pdfReader.Close();
          }
          return _stringBuilder.ToString();
      }