linux manual location
 

where can i find the documentation of a program, and what are utilities to read it?

On command-line, use 'man <command>' (try 'man man' for a start). In a graphical environment, there may be other tools to display these man pages. I think the KDE helpsystem allows searching and browsing of manpages. The files are located in /usr/share/man and several other locations on my SUSE system (type 'echo $MANPATH' for the complete list).

Often there is a separate package with the documentation that you can install.

This documentation is often located in /usr/share/doc/packages/ and might be text files, or html files, and sometimes pdf files.

For example, if you have it installed, you might find the starting point for PAM documentation here: /usr/share/doc/packages/pam/html/index.html

One way of locating documentation is to use the locate command.
locate pam | grep '/doc/' | grep index
/usr/share/doc/packages/pam/html/index.html
/usr/share/doc/packages/yast2-pam/autodocs/index.html

If you have apache running, you might find documentation for cups at http://localhost:631 (13 separate manuals)

For thorough samba documentation, install samba-doc. For some distro's the documentation may be included with samba-swat and accessible through http://localhost:901 .

There is a directory of kernel documentation included with the kernel-source.

You can print out the important man pages using the -Tps ( or -t option on some systems ).
For a nice printout of info manuals, you could install the source packages you are interested in and run 'tex <package>.texi' in the DOC directory of the source.

There is a great web site of linux how-to's, man-pages, magazines and books. http://www.tldp.org