1) Open command Prompt (type cmd in run).
2) You may change to any directory where you want to save that file.
3) Type notepad filename.txt:StoreHiddenData then press enter. here filename is name of file for example if i want to create a notepad file of name secret then i will write notepad secret.txt:StoreHiddenData. This will create a text file secret.txt.
4) A message will be pop up Cannot find the D:\secret.txt:StoreHiddenData.txt file. Do you want to create a new file?, click OK button to proceed create the new file.
5) A notepad will be pop up. Type data that you want to hide from others. Save the file and you are now successfully creating hidden data for this file.
6) close cmd.
A notepad file secret.txt is successfuly created which contains hidden data. When you open secret.txt, it seems empty. Actualy your data is hidden so you are not able to see it.
If you want to see your hidden data then open cmd and type notepad secret.txt:StoreHiddenData. A notepad file will be pop up which contains hidden data.