Portable document format is one of the most popular file formats on the web. Of course Adobe is the market leader for PDF. However, there are lot of free alternatives around. Here are some free pdf viewers for ubuntu.
Home Page http://projects.gnome.org/evince/
Evince is a document viewer for multiple document formats. It currently supports pdf, postscript, djvu, tiff and dvi. The goal of evince is to replace the multiple document viewers that exist on the GNOME Desktop with a single simple application.
Evince is installed by default on the ubuntu desktop.
Home Page http://www.foolabs.com/xpdf/about.html
Xpdf is an open source viewer for Portable Document Format (PDF) files. Xpdf project also includes a PDF text extractor, PDF-to-PostScript converter, and various other utilities.
On ubuntu you can install xpdf as
$ sudo apt-get install xpdf
Home Page http://okular.kde.org/
This is from the kde stable . Okular is a universal document viewer based on KPDF for KDE 4.
On ubuntu you can install okular as
$ sudo apt-get install okular
d) epdf viewer
Home Page http://trac.emma-soft.com/epdfview/wiki/Download
epdf viewer is lightweight pdf viewer based on poppler libs. The aim of ePDFView is to make a simple PDF document viewer, in the lines of Evince but without using the GNOME libraries.
On ubuntu you can install epdfview as
$ sudo apt-get install epdfview
Home Page http://wwwthep.physik.uni-mainz.de/~plass/gv/
gv allows to view and navigate through PostScript and PDF documents on an X display by providing a user interface for the ghostscript interpreter.
On ubuntu you can install gv as
$ sudo apt-get install gv