How to Pause/Resume a process in Linux

To pause the process

kill -STOP <PID>

To resume it

kill -CONT <PID>

Ctrl + z (SIGTSTP) from the shell stops (nowaday we will probably use the term "suspend", which the man page of bash does) a process. The process can be continued ("resumed") with the commands fg (in foreground) or bg (in background).

kill -9 doesn't stop a process, it kills it (SIGKILL). I mention it, because wording here is ambiguous.