I have been asked How I make invisible ink.
First I enter the whole document with the parts that I want to become invisibile still showing.
Then I select the part I want to be invisible, and hit the text color button -- the colored A on the tool bar -- and color the text the same as the background color, in most cases, white.
When it prints, the text become invisible against the same colored background. When you drag the cursor over it, it becomes "highlighted", and visible.
Example >>> Isn't that fun? <<<