man man

1   Executable programs or shell commands
2   System calls (functions provided by the kernel)
3   Library calls (functions within program libraries)
4   Special files (usually found in /dev)
5   File formats and conventions, e.g. /etc/passwd
6   Games
7   Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7), man-pages(7)
8   System administration commands (usually only for root)
9   Kernel routines [Non standard]

* apropos (man -k) - search the manual page names and descriptions

$ apropos icmp
icmp (7)             - Linux IPv4 ICMP kernel module.
ping (8)             - send ICMP ECHO_REQUEST to network hosts
ping4 (8)            - send ICMP ECHO_REQUEST to network hosts
ping6 (8)            - send ICMP ECHO_REQUEST to network hosts

* -s section

$ apropos -s 8 route
ip-mroute (8)        - multicast routing cache management
ip-route (8)         - routing table management
route (8)            - show / manipulate the IP routing table
routel (8)           - list routes with pretty output format
tc-route (8)         - route traffic control filter
tcptraceroute (8)    - print the route packets trace to network host
tcptraceroute.db (8) - print the route packets trace to network host

* -a (and) Only display items that match all the supplied keywords, The default is to display items that match any keyword.

$ apropos  -a remove director
remove (3)           - remove a file or directory
rm (1)               - remove files or directories
rmdir (1)            - remove empty directories

* whatis (man -f) - display one-line manual page descriptions

$ whatis getopt
getopt (1)           - parse command options (enhanced)
getopt (3)           - Parse command-line options

$ whatis route
route (8)            - show / manipulate the IP routing table

$ whatis ip-route
ip-route (8)         - routing table management

man -K Search for text in all manual pages

$ sudo apt install groff
$ man -Tpdf man > man.pdf