How are the file formats different?

Question

Programming

A little embarrassing, but I want to understand the situation.
I have been programming for a long time, mainly web application development.
I use interpreted languages, I rarely compile.
If you take html, py or js, php ... Everything is clear here - all content is described by text.
If we take an executable file and open it with a notepad, we will get quacos. an executable file is a machine code file of zeros and ones, which in turn we can recognize in some editors.
And as for PDF, excel, doc... they are not executable, are they? And I can't open it with a notepad... And when generating, the xml backing is used.
How are they coded? What about JPG? and image formats. And the video?
Thank you!

Answer 1

they can be anything different. starting from the internal device and ending with compression methods.
if the format is open, you can open the specs and compare with other formats.
if the format is closed, reverse engineering is in your hands.