>In Word, when typing, if I type the : character, Word automatically inserts a space before the character. How can I avoid that?
Perhaps, if you press "Undo" often enough, Word will remember - but I am not so sure about this.
OTOH, Word has a list of expressions to replace automatically. I find it under "Tools | Autocorrection" (translated from Spanish). Perhaps you have the colon in that list.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)