Crack copy protected PDFs in Ubuntu Linux

In this example we 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

Source: blog.dipinkrishna.info