Question

Opening the door, he asked for my permission to come in. (Make it complex)

Answer 1

Answer:

After opening the door he asked me if he could come in

Explanation:

Answer 2

Complex sentence:

While opening the gate, he asked for my permission to come in.

Explanation:

              A sentence could be termed a complex sentence if it has one independent clause and one dependent clause. It could be used when more information is to be communicated or when the main point of the sentence is to be modified.

But the meaning remains unchanged.

E.g., The food cooled down, I used the microwave to warm it.