I had needs to modify the pdf. For not going to run into wrongful dismissal with the editor Adobe PDF I have tried a little 'what was between open source and I found this very good program.
Is called PDFedit and for those who use * buntu 7.10 is present in the repo. Just take a long terminal
sudo apt-get install pdfedit
and you're done (or go to synaptic and search for the package pdfedit).
The installation will create a shortcut in Applications / Graphics / PDFedit (if there were you can boot from a terminal with the command pdfedit).
The graphics will not be the best but the operation is good.
Positive note: I was allowed to export images and text with a disarming simplicity.
Note negative: the satisfaction is not the most often seen, especially with PDF files and a little 'heavy, he "crashed" and the one and kill the transaction.
For the texts you should have the foresight to select a few lines at a time if you want to copy them in external files may recur because the problem described above.
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pdfs you can also change with the next version of Inkscape available on Ubuntu 8.04