What is PDF ?Portable Document Format (PDF) file is a self-contained cross-platform document. PDF is an open standard for document exchange. PDF documents look the same on the screen and in print, regardless of what kind of computer or printer someone is using and regardless of what software package was originally used to create it.
PDF files include complete formatting of the original document; including the text, fonts, graphics, and other information needed to display it. PDF files are highly compressed, allowing complex information to be downloaded efficiently.
You read a PDF document using a PDF reader / viewer.
There are a number of free PDF viewers available in Linux as listed below.
Evince Document Viewer
Evince is a document viewer for multiple document formats. Evince aims to replace the multiple document viewers that exist on the GNOME Desktop with a single simple application. Evince supports the following file formats - PDF, Postscript, DjVu, TIFF, Dvi, XPS, SyncTex support with Gedit, and Comic books (Cbr,Cbz,Cb7, and Cbt). All PDF documents including password protected ones can be viewed in Evince.
Evince is the default document viewer in GNOME centric Linux distributions such as Ubuntu and Fedora.
Evince website - projects.gnome.org/evince/
Okular is a universal document viewer for KDE 4. Okular is to KDE 4 what Evince is to GNOME. Like Evince, Okular also supports a number of document formats. Apart from being a Free software PDF reader, Okular also support the following file formats - PDF, Postscript, DjVu, CHM, XPS, ePub and many others. Okular is based on KPDF.
If you are using a recent KDE centric Linux distribution like Slackware, Okular should be installed by default. However, you can also install it from the respective repository of your Linux distribution.
Okular website - okular.kde.org
KPDF is a Free PDF reader for KDE 3. The latest stable version was released on August 26 2008 as part of KDE 3.5.10. KPDF is based on another open source PDF viewer - Xpdf.
KPDF is outdated. Okular is far more versatile and actively maintained.
KPDF website - kpdf.kde.org
Xpdf is a Free PDF viewer that has a low memory footprint. Apart from a PDF viewer, Xpdf suite also includes a PDF text extractor, PDF-to-Postscript converter, and various other utilities. It runs on a number of OSes including Unix, VMS, OS/2, Windows, and of course Linux. Xpdf is an ideal choice of PDF viewer for low end machines that have low memory.
Xpdf has been widely ported to various non-UNIX systems such as RISC OS, BeOS, Amiga, EPOC (the Psion operating system), OPIE (embedded Qt on iPAQ/Zaurus hand helds), and PalmOS 5.x.
Xpdf package is included in the repositories of most Linux distributions.
Xpdf website - www.foolabs.com/xpdf/.
We all know, Adobe Reader is the de facto standard for viewing PDF documents. Adobe has released its popular Adobe Reader for Linux as well. However, it is not open source.
The latest version of Adobe Reader for Linux (as of this writing) is Adobe Reader 9.4.7.
While booted into Linux, visit the following link - get.adobe.com/reader/ - to download Adobe Reader for your Linux distribution.