Extent curve to plane

Hi everybody

I need to extend some rebuild polylines (now curves) to a certain plane. Until now I have been trying to do it by hand but this takes ages. Is there a way to make that the curve snaps automatically to the reference plane? I have put a tick on the gumball at snappy dragging but this didn’t change anything. It would be great if somebody could help me, thanks!!
20210819_New_version_recovered_ohneMesh.3dm (5.6 MB)

Cheers
Isabel

did you try:
_extend IP

_extend will let you choose boundary Objects
IP (as a boundary) is an Infinity Plane … set it with 3 Points for example
(to get a bigger IP, you may want to additional objects to your file - that define the maximum needed size)
klick on the lines to extend

not 100% sure if this helps - if not, you may want to sketch on a screenshot to more specific describe the needed workflow.
kind regards -tom