I was told there are Alt codes to add spanish letters and
symbols to word documents.
Correct.
Does anyone know where a list of these may be found?
Checked Google yet?
However, there's a better solution. Go to the Control Panel, to
Regional and Language Settings, Languages, Details, add
US-International, remove others since you won't need them anymore,
reboot, and you'll have access to international characters instantly.
To put accents over letters, type ' followed by the letter, say e, and
you'll have the letter é, for instance. Umlauts are created by typing
", followed by the letter, thus you can type Ä, Ë, Ã, Ö, Ü, and the
lower case versions of these. The German ß is created by holding down
the right-hand ALT key while typing an s. ¿ and ¡ by doing the same
(right ALT key) and ?, or !, respectively.
Hold down the right ALT key, and/or combine it with SHIFT, and see
what letters come out.
¡²³¤€¼½¾‘’¥×¹£÷ <---- numeric line, combined with ALT and/or SHIFT
äåé®þüúÃóö«»/ÄÅÉÞÜÚÃÓÖ <---QWERTY, ditto
áßðø¶´Ã§Ãذ¨ <---ASDF
æ©ñµç¿Æ¢ÑÇ <--- \ZXCV
Any letters not in the list above, you're SOL and on your own

It's actually rather intuitive, especially of you don't need the whole
set