Semi-related tip: I despise protected pdfs with a passion. Especially when you download a datasheet and you can't add annotations or highlights to it. So, how to remove this protection? One way is to print to postscript and convert back to pdf, but then you can't copy text from it.

Here's how (on windows): download qpdf (http://qpdf.sourceforge.net/) and run

     qpdf.exe -decrypt encrypted.pdf woho.pdf

I made a small batchfile since I never remembered that syntax,

    # usage:
    #    decrypt.sh mypdf.pdf
    # the decrypted file will be named mypdf.pdf, while the old encrypted is now mypdf.pdf-encrypted.pdf
    # 
    echo pdf to de-secure: $1
    read -n 1 -s -p "Press any key to continue"
    mv "$1" "$1"-encrypted.pdf
    qpdf.exe -decrypt "$1-encrypted.pdf" "$1"
    echo encrypted file is now named: $1-encrypted.pdf
    echo decrypted file is: $1