Hi gchick,
Here's two ways for Word:
1. Select a piece of text and insert a hyperlink to it and insert your message as the tip text
2. replace a piece of text with an Autotext field and insert your hidden message as the tip text. Code the field along the lines of:
Code:
{AutoTextList "replaced text" \s NoStyle \t "Put the hidden message here"}
In both cases, your hidden text will only display while the mouse hovers over the hyperlink/autotext. With the autotext approach, be aware that the 'display text' will disappear from the field code once it's updated and gets added to your autotext entries. The advantage is that it doesn't get the usual hyperlink formatting.
Another way you could hide some text is by placing it inside a SET field in the header/footer. For example, if you create a SET field coded as:
Code:
{SET _Hidden "This is the hidden message"}
Your message will only be retrievable by toggling the field code display, or inserting a cross-reference to it (and that '_' in the field keeps the bookmark hidden from view unless to user is savvy enough to select the 'show hidden bookmarks' option under Insert|Bookmark). Putting the field into the Header/Footer minimises the risk of it being deleted.
Yet another way is to define a custom document property to hold your hidden text (via File|Properties|Custom), which would then be accessed via Insert|Field > DOCPROPERTY.
None of these specifically hides a text string in-line with other text in the document (for which formatting the text with the same colour as the background will do), but all allow different ways to 'hide' and 'retrieve' text in a document.
Cheers