Use two simple commands to convert a protected pdf into an unprotected pdf.
Here in this example i assume the protected pdf file name to be ‘protected.pdf’.
Now open your terminal and type.
$ pdftops protected.pdf out.ps
$ pstopdf out.ps out.pdf
The out.pdf will be your unprotected PDF.
If you don’t have pstopdf and pdftops installed then type this at terminal to install them.
$ sudo apt-get install context