Are ubuntu software center sources different from apt-get / synaptic?

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http://askubuntu.com – I'm trying to download master-pdf-editor package from official repositories. All sites report that it's easy to do: just download it from ubuntu software center. I can't install the software center, so I'm trying to install it via apt-get or synaptic, but I can't find the package in the repos... Can anyone help? (HowTos)