The edges of damaged books can be separated, scraped flat with a knife, and then wetted with a brush. The paper used for repair is also wet, and then it is torn, and the edge of the paper will protrude a little fiber. The edge of the book and the repair paper will be stuck together with adhesive, and the repair position will be very consistent. If the file to be repaired is very thick, it is necessary to pad an offset plate under the repair paper, make a small hole with a needle, and then tear it along the boundary, so that the interface to be repaired can be tight and firm.
This is more professional than most people can do.