Razor sharp with sandpaper will take a while but you can do it. It all depends on your edge bevel. You will get many answers but the majority of knives have an edge angle anywhere from 15 to 30 degrees. Of course, that wont help you if you dont have anyway of checking an angle. However using sandpaper, if you wrap it or tape it to a flat surface, I use a paint stir stick, you can treat it like a kitchen steel. Use the finest files you can to get to close to your final edge. By this point it should be noticeably sharp, now switch to the sandpaper. If it cuts paper without too much pressure, start with 220 or higher grit paper. Glide the edge of the knife along the paper with only the weight of the knife as pressure. After a couple of passes, check for sharpness and move on to a higher grit. After 1500 you are really just polishing the edge which makes the knife glide through things easier, instead of making the sharp edge, sharp. If you can afford it, you should look into various sharpening systems be it stones (oil or water), diamond plates or ceramic sticks. It may take some practice, but once you get it, you will be the one everyone goes to for sharpening. Good luck, have fun.
