PDFedit allows to edit PDF document completely.
You can change either raw pdf objects (for advanced users) or use predefined GUI functions. Functions can be added as everything is based on a scripts.
How to install PDFedit in ubuntu:
Code:
sudo apt-get install pdfedit
p.s. The program didn't really work well for me. I didn't manage to change text elements in my PDF document. Also I wasn't able to undo the changes. I don't really like PDFedit at all.