So, about the vertex paint. You can use vertex paint to paint the part of the door you want to affect with the scratches if that’s what you’re looking for.
Basically, you create a material, you add a vertex color node and you connect it to the color input or to a viewer node. Then you pick a shade of grey and you start painting on the model. Lastly, you can use this vertex color information to mask the part you want to keep clean and the part you want to look scratchy.
If you don’t need a particular area but just an overall feeling of scratches across the surface, you can simply use a roughness map.
Here are a few screenshots.
Vertex paint example:
result
Plain roughness material
Lastly, with a cavity map or curvature type of effect
For the last example you can follow the tutorials I posted above or this one here, which is probably faster (same method I used in the screenshot)
If none of this works, please, post some screenshot or reference of what you’re trying to achieve.