Modify an upload stl file

I’m a new guy here!
I need help to modify an upload stl file on rhinoceros?
Is it possible to do it?
Thanks a lot!!

Welcome @nuancesgourmandes
Start here.

Yes, rhino can modify stl files,

BUT, what is it your are trying to do and what type of mods are you trying to make?

what is your end goal, (render, prints, data transfer, animation?)

screen shots and more info would help.

i need to cut an stl file to put in my mold
after i print it
please find in attachment some screen shot about it
thanks a lot

if you are using v6 try the mesh boolean split-

both parts have to be closed for this to work.

Thank you,
sorry, but can’t do it!!!
link for the download 3d file :
it’s better to see my problem!!
thanks a lot