Unknown encryption type R = 6 error

[iamSathishMohan]

Summary of the issue

While reading the PDF2.0 version of pdf document using the PdfReader throws an error like Unknown encryption type R = 6

Environment

iTextSharp.LGPLv2.Core version: 1.7.3
.NET Core SDK version: 3.1 & 5.0
IDE: Visual Studion Community 2019

Example code/Steps to reproduce:

var reader = new PdfReader('c:\samples\sample.pdf')

Output:

iTextSharp.text.exceptions.InvalidPdfException: 'Unknown encryption type R = 6'

Exception message:
Full Stack trace:

[slavat]

A related issue https://github.com/LibrePDF/OpenPDF/issues/375