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)
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"