how can i turn off microsoft word spelling error indication (those red
lines under misspelled words) for a single document, and retain it for
all other documents?

Greetings kwaaker-ga!

I've recently had to do this for a resume that I needed to email out
and wanted to hide those red/green squigglies.  I messed around Word
for awhile and I finally found where Microsoft hid the option.

This solution will let you hide errors in a single document but still
have spelling and grammar check turned on for all other documents. 
This setting also saves itself along with your document so everyone
who opens your Word document will also not see any of those red/green
lines.

First, once you open your document, hit Ctrl+A to select all
objects/text in your document.  Goto Tools menu, Language, Set
Language.  Simply check the box that says "Do not check spelling or
grammar".  Then click OK.

Hope this is what you were looking for.  Let me know if you need
additional clarification.

Thanks,
mrbuzz-ga

fabulous.  exactly what i was looking for.  i've wondered for quite a
while how to do that.

Here's another way to do the same thing. Look at the status bar at the
bottom of the screen (above the taskbar). It should be a series of
boxes, some with text in them, some empty. The second box from the
right might have a picture of a little book in it, or it might be
empty. Simply right click on that box and select Hide Spelling Errors
and then do the same for Hide Grammatical Errors. You don't need to
highlight any text either, as this hides all the errors in the
document.