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
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