This program is untested by me,
then why are you suggesting it to others?!
then we have the statement on the site itself:
I am no cryptanalytic, and wrote Paperback quickly and without much thinking about the strength of the code.
neither one is going to give me any confidence to want to even check out what this project is about.
also it is not published on any public code sharing platforms such as Github for review and discussion. the source seems to be only available as a zip file on the same site which means even if it has any problems it won't be reported publicly and you won't find out about them unless you spend a ton of time reviewing code yourself.