Creo Interactive Surface Design (Style) > Curves > Editing Curves > About Making Curves Planar Between Their Endpoints
  
About Making Curves Planar Between Their Endpoints
You can make free curves planar between their endpoints. When you make curves planar between their endpoints, the curves and their endpoints lie on a plane that is perpendicular to the active datum plane. If necessary, free tangents are modified while the curves are made planar between their endpoints. The curves do not maintain history when they are made planar between their endpoints.
 
* You cannot make curves planar between their endpoints if they contain constrained internal points or endpoints with tangent constraints.