These parts are 3D printed with a smooth surface and without noticeable build lines.
3D printed parts will not have any mold lines but may have some minor bumps on the rear faces of the model from where the supports were attached. The best way to remove them is to sand or file any remaining nubs or bumps. You can also use a sharp hobby knife with a new blade and work by taking it off in small layers. Approach it very lightly, less is more when working with 3D prints.
You can soften the prints by heating them for 30 seconds in a cup of hot water (tea/coffee hot) this will make it easier to remove the nubs without chipping. You can also heat the parts to remove any warping or slight bends in the part.
Before painting wash the prints in warm soapy water to remove any residue. Bent or warped parts can also be heated in water then gently straightened.
These parts will need to be attached with CA style super glue. Krazy Glue, Gorilla Glue, Zap Cap will work well. Plastic model cement such as Testors brand or Games Workshop model glue will not work on resin or 3D prints.