I eat a lot of junk food. If I eat a lot less calories (but its still junk food) will I lose weight?

You might. Eating junk food you will loose both essential muscles and body weight by reducing calories. So in the long run will have altered body composition which would affect your heart, intestines and brain. If you eat lot of junk food watch my video on 5 steps to great health at drbrown. Us and maintain proper ph, detox frequently and replace vitamin D3 and nutrients.
No. Diet & exercise. Make sure you exercise at least 30 minutes a day, don't skip meals, avoid soda, juice, dairy, alcohol and fried foods. Eat a healthy well balanced diet! Also water, organic vegetable broth, green leafy vegetables, natural pickles, apples are great to fill you up so you dont feel hungry and they are very low in calories.
Maybe yes. A calorie is a calorie, regardless of where it comes from, so a diet of junk food will still cause weight loss if the total calories eaten is fewer than the calories used up during the day. Some types of "junk food" are always junk food, while other types of "junk food" are healthy in small quantities and only become junk food if eaten in excess. Good quality food is needed for balanced nutrition.
Junk food and weight. Any excess calories you eat in (carb, protein, fatty foods) will be banked by the body as fat. The body needs protein from food (cows get protein from grass as they can digest grass). We need protein and greens-veggies and minimize carbs to loose weight smartly. When you are hungry, the body uses the stored fat to feed itself (pull saved money out of the bank savings). Learn to eat less smartly!