ubuntu上移除忘掉的pdf密码

转自：http://townx.org/blog/elliot/removing-password-pdf-linux

Removing a password from a PDF on Linux

Sun, 2007-08-12 09:31 ― elliot

I just bought a  PDF, legally, from a publisher's website. However, in their wisdom, they decided it would be a good idea to password protect all legally-purchased  PDFs. This means that each time you open the  PDF using Acrobat Reader, you have to remember and type in the password to read it. (Evince, the built-in  PDF viewer in Linux, allows you to permanently save the password, but I tend to use Acrobat as it copes better with some  PDFs.)

So, if you know the password for a  PDF and want to remove it, you can use the command line tools  pdftops and ps2pdf to free your  PDF from its chains.

Install pdftops. On Ubuntu, you can do:
apt-get install xpdf-utils
Install ps2pdf. I think this is already included with a default Ubuntu.
Convert the PDF to a postscript file, using the password:
pdftops -upw <password> <file>.pdf
Convert the resulting postscript (which is now sans password) back to a PDF:
ps2pdf <file>.ps

The only thing you lose are any  PDF-specific features which don't translate to postscript, e.g. hyperlinks.

Remember, this only works if you know the password for the  PDF: it doesn't break the  PDF password for you.