I know what you mean. I've done this before, but I still die, which needs to be repaired slowly. The outline of the seal and signature is not obvious, so I can just trim it roughly when I repair it.

If your document paper is white, you should turn up the brightness of the scanned white paper, and the chapter is usually red, so that the contrast is strong. Just use the magic wand to select the area. If you are familiar with PS, the method tells you how to operate it.

In short, the details of stamping and signature need not be perfected. If you don't believe me, you can see if the outline of your document is clear.