Although you can export DXF files from BikeCAD as described at: bikecad.ca/dxf_export, there is currently no way to import a DXF or DWG.  What you can do is save a CAD drawing as a bitmap in BMP, GIF, JPG or PNG form and import that into BikeCAD Pro.  When you import a bitmap it gets underlayed behind your design, so it's easy to use as a reference.  This process is explained at: bikecad.ca/import_photo.  Note that a photo is used in that example, but it could just as well be a CAD drawing.