I am not able to use the pen and draw a line in the map, is this not a feature in the RM? I want to make lines where pipelines are laying at seabed in a harbour where i am doing a job.

Yes, you can do it as part of a map project. Take a look at this post for more information: https://reefmaster.com.au/index.php/forum/support/2061-drawing-lines-between-to-gps