How to embed one dll into another?

Question

C++ / C#

See I have two dlls and their sources.
Tell me how to put the code of the second dll into the first one?
To then collect the first one and the output was 1 dll out of two.
I don't know much about C so this is a stupid question.

We have one format in php, and in the plus there are both .h and .cpp and some other ones.
Well krch difficult yet. Tell me how, in theory, as I think:
Move all the source files of the second to the first.
Connect main of the second to the first and call this main.
Well, how does the main of the second file find out where its file is, or does it look nearby?

Answer 1

Understand what functions are needed and transfer their code from one source to another. In this case, you need to take into account dependencies on other, non-standard libraries, if any.