I was wondering if there is a pdf reader-writer-publisher-editor that can add text, highlight, shapes and general edit an existing pdf document.
Something like Nitro in windows.
There are several FOSS options out there, none of which come close to the functionality of editors such as Foxit PDF Reader under Windows or commercial solutions under Linux. That's why I prefer to run Foxit via PlayOnLinux.
As far as native applications are concerned, Master PDF Editor is probably the most advanced free (as in beer) PDF editing suite available in Ubuntu right now. It's available from the Ubuntu Software Center but requires you to register an account with Ubuntu before installing.
A few months ago I stumbled on Quoppa PDF Studio, a commercial PDF editing solution that runs natively on Linux via Java. It comes with a very impressive featureset and is very close to Adobe Acrobat in terms of PDF editing functions. However, I have found PDF Studio to be a bit less stable than Adobe's solution when editing very large PDF files (≥ 500 pages).
Other than that I would say that PDF Studio is a very good, albeit expensive, piece of software and probably the best PDF editing suite out there on Linux right now.
You can download a free trial version here. It doesn't come with a time restriction. Instead, edited PDFs are automatically watermarked by the software to indicate that you're using the trial edition.
LibreOffice 4.0 opens PDF files in LibreOffice Draw where you can make all kinds of edits. I just used it to enlarge 80 images and move them around; it worked great!
If you are using Ubuntu 12.04, 12.10, or 13.04 then you probably have version 3.5, which does not have this feature. As I did, you can now force Ubuntu to upgrade to version 4.0 by typing the following in a terminal (press enter after each line).
If you don't have LibreOffice installed for whatever reason, then instead of the last line, type this.