When a friend says, "Hope you are doing well," it is usually an expression of goodwill and concern for your well-being. They are expressing their desire for you to be in good health and happiness. It's a common way for people to check in on each other, especially if they haven't been in touch for a while or if there might be some reason for concern.
This phrase is often used as a casual greeting in conversations, emails, or text messages to show that the person cares about your welfare. It's a way of expressing kindness and letting you know that they are thinking of you. In response, you might say something like, "Thank you! Yes, I'm doing well, how about you?" or simply acknowledge the message with appreciation.