Question

I need to find all files with specific filename(for example main.css) in folder and all subfolders and then do something with it(eg. rename, move, delete, add text line, etc)

Answer 1

This is what you need:

for /R %f in (main.css) do @echo "%f"

Naturally you would replace echo with whatever it is you wish to do to the file. You can use wildcards if you need to:

for /R %f in (*.css) do @echo "%f"