iText - read PDFs created with an unknown random owner password

I'm getting the following exception when excecuting this code:

public byte[] watermarking(byte[] orig) throws IOException {
        PdfReader pdfReader = new PdfReader(orig);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        PdfStamper pdfStamper = null;

        try {
            pdfStamper = new PdfStamper(pdfReader, baos); //exc here
            ...
            }
            ...
        } catch (DocumentException var8) {
            ...
        }
    }

Exception:

11:43:11,094 ERROR [de.mlp.xbg.pa.rest.SessionRR] (http-/127.0.0.1:8081-6) PdfReader not opened with owner password: java.lang.IllegalArgumentException: PdfReader not opened with owner password

I checked other threads regarding this topic and it seems that the easiest solution is to add PdfReader.unethicalreading = true;

However, I'm forced to use iText 2.1.7 or older (com.lowagie iText) and not iText 5.0.0 or newer (com.itextpdf iText). PdfReader.unethicalreading does not exist in the old version of the library.

Here there seems to be a workaround to make iText to ignore password with a disclaimer:

I leave legal issues up to you by executing the code below.

public static PdfReader unlockPdf(PdfReader reader) {
    if (reader == null) {
        return reader;
    }
    try {
        java.lang.reflect.Field f = reader.getClass().getDeclaredField("encrypted");
        f.setAccessible(true);
        f.set(reader, false);
    } catch (Exception e) { /* ignore */ }
    return reader;
}