Adobe's PDF format is one of the most ubiquitous open standard file formats available today. It is no surprise that Linux has various software that supports the file format. Whilst this is definitely not an exhaustive guide to all PDF tools on Linux, it will give you a glimpse of what's out there.
First stop, PDFEdit, a tool to edit PDF documents. Installing it is done by a simple apt-get.
PDFedit is one powerful GUI and CLI based tool that is scriptable. So those the shell scripting junkies, this may be the best tool for you.
Another PDF editor for you is from Sun Microsystems and it is dubbed as the PDF Renderer. It is a completely Java-based tool that makes it portable across multiple platforms. See the tool running in a totally immersive, 3D environment. :)
So these are just two PDF editors for you. If you prefer one over the other or prefer a completely different one, please do share it with us.