Can you download anything to keep your files safe from your sisters?

can you download anything to keep your files safe from your sisters?like say you have private emails from your friends which you keep saved in microsoft word, is there anything you can download or get that would keep them files safe from your sisters, say if you needed a security code to open it up?please anyone... show more can you download anything to keep your files safe from your sisters?like say you have private emails from your friends which you keep saved in microsoft word, is there anything you can download or get that would keep them files safe from your sisters, say if you needed a security code to open it up?please anyone know?THanks!!
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