If you really don’t want someone to read what you’ve written in any way you can’t use tipex (whiteout) since the inpression of the pen or pencil might be visible through the paper. Scribbling over with straight lines might still let someone pick out letters. The best way is, with the same writing device preferably, to write random words/letters over your text until it’s sufficient obfuscated. It becomes almost impossible to discern what was originally written.