Formula that checks a string trough the whole document for a match?

Hi! I wanna crete an input form that would check if the string the user enters is present anywhere else in the document(trough all sheets) and I'm looking for a formula that that would enable that.
Probably the easiest would be with conditional formatting so the cell content then turns red if the string is present and it turns green if it's not present.
Thanks!

EDIT: Oh, not Excel, but Google Sheets