To support the print of encrypted documents, you have to decrypt it first.

To do so, you need to change PDFViewController.printPDF as follows:

public void onWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal,
               WriteResultCallback callback) {
   InputStream input;
   OutputStream output;
   try {
      String mDocPath = m_view.PDFGetDoc().getDocPath();
      if(!TextUtils.isEmpty(mDocPath)) {
         if(m_view.PDFGetDoc().IsEncrypted() && m_view.PDFGetDoc().SaveAs(m_parent.getContext().getFilesDir() +
               File.separator + "temp.pdf",true))
            mDocPath = m_parent.getContext().getFilesDir() + File.separator + "temp.pdf";

         input = new FileInputStream(mDocPath);
         output = new FileOutputStream(destination.getFileDescriptor());
         byte[] buf = new byte[1024];
         int bytesRead;

         // check for cancellation
         if (cancellationSignal.isCanceled()) {
            callback.onWriteCancelled();
            input.close();
            output.close();
            return;
         }

         while ((bytesRead = input.read(buf)) > 0) {
            output.write(buf, 0, bytesRead);
         }
         callback.onWriteFinished(new PageRange[]{PageRange.ALL_PAGES});

         input.close();
         output.close();
      } else
         callback.onWriteFailed(m_parent.getContext().getString(R.string.pdf_print_not_available));
   } catch (Exception e) {
      e.printStackTrace();
      callback.onWriteFailed(e.toString());
   }
}

And add the onFinish callback:

@Override
 public void onFinish() {
     super.onFinish();
    if(m_view.PDFGetDoc().IsEncrypted())
        new File(m_parent.getContext().getFilesDir() + File.separator + "temp.pdf").delete();
 }