My baby is 4 months old and I'm starting to introduce bottle to him with my pumped breastmilk but he is refusing and cries endlessly. How can I make him take the bottle?

Your baby may be associating you with latching. If so, it's natural for him to reject the bottle when you're around. Try to get someone to bottle feed him instead. If need be, leave the house for 3 hours or so such that he does not have the choice but to take the bottle. You can try various bottle teats. Nuk latex teat worked for me. I heard Pigeon peristaltic is not bad too.