pdfcrack does not detect encryption on one of my files:
Error: Encryption not detected (is the document password protected?)
The content of the file is copyrighted so I can not post it here.
Please try with the latest version which should fix the problem you are seeing if the pdf is supported.
If it does not help and the revision is less than 6, please contact me privately and we should be able to work out a solution for you.