Get method to pack/unpack a file?

Question

C++ / C#

People, hello everyone!
The topic is new for me, tell me, having a file exactly a file not an archive in a binary format / form, and the same file but in a text format (that is, decoded), how to use these two files to find a method for compiling a file into a binary format from text and vice versa ?
Are there programs that parse two files and suggest a method?
How in general to find a method of decompilation and compilation, having an initial and final file?
Thank you in advance.
PS Dass, I had to tinker with the understanding and operation of the Hex editor, but surprisingly it turned out to be very easy, I understood the whole essence of creating a file structure when compiling, quickly bungling the unpacker, I finally got what I wanted.
It would be necessary to write a normal tutorial on Habré on working with binary files not archives in the Hex editor, otherwise there is nothing for the people at all.
15432 Thank you!

Answer 1

Attach an example file, maybe I'll find out the algorithm.
If there is no packer itself, look at the contents. The title may contain a hint. And so, it is very difficult to define an arbitrary packing algorithm.