You can underlay and snap to 2D geometry stored in PDF files.
Underlays are similar to attached raster images in that they provide visual content but also support object snapping and clipping. Unlike external references, underlays cannot be bound to the drawing.
Use the Visor to Work with Underlays
If you select an underlay the PDF Underlay visor is displayed. The visor contains options for adjusting, clipping and displaying underlays. The visor is dismissed automatically after the underlay is deselected.