Remove password from password protected pdf file

First convert the file to postscript (ps) file with poppler:

pdftops [your_protected_pdf_document.pdf] out.ps

Now reconvert it to pdf with Adobe Distiller. There, password has been removed from the pdf file.

On Linux do this:

pdftops {your_protected_pdf_document.pdf} out.ps
pstopdf out.ps broken_protection_pdf_document.pdf 

Credit:
http://stackoverflow.com/questions/14233756/remove-printing-protection-from-pasword-protected-pdf-files