The only programs that I know where you can copy then paste into Xara3D are Xara X¹, Xara Xtreme, and Xara Xtreme Pro.

There are other vector editors available but none of them that can paste directly into Xara3D, that I am aware of.

Most other vector graphic applications are expensive. There are freeware and shareware vector editors available but I have very little experience using them with Xara3D.