Copy clips from one file to another

[Namna]

Si, on peut le faire !

Yes, we can do it !

Save part of timeline in "mlt" format

No, but you can: turn on ripple all tracks navigate to start ShiftI to ripple trim in navigate to end point ShiftO (oh, not zero) to ripple trim out File > Save As… It is possible you need to tweak some of the above, but that should give you the general idea. You might also want to clear the playlist before saving depending on what you are doing with it.