[Unum]

Hello, I've been researching this topic and someone sent me here. I begun taking notes on some books I need for a work, both in my ebook and on PC.
When I am using the windows it work like a charm and I find it insanely useful (an even though I'm yet learning to take full advantage of this feature) to just select the text, choose the color and maybe write something else.
But this option seems totally missing on my linux laptop (I have the library on a pendrive), is that normal? Thanks in advance for any help.