PDFTK: Owner password required error

Problem

You try to manipulate a PDF file using PDFTK and it throws the following error:

Error: Failed to open PDF file:
   101.pdf
   OWNER PASSWORD REQUIRED, but not given (or incorrect)

Solution

The PDF files for which PDFTK prints this error might be password protected or encrypted.

If you can open and view the PDF file using any PDF viewer then it might mean that the PDF files are protected or encrypted with an empty password. To be able to apply PDFTK on these files, you will need to remove the protection or decrypt the files. One way to do this is using the QPDF tool as described here.

If the PDF file is password protected and you know the password, then open it in any PDF viewer by entering the password. Next print the PDF file to a PDF file. The resulting PDF file can be used with PDFTK.

Tried with: PDFTK 1.44