That explains why it happened.
I doubt whether there was any problem with the configuration of
WinWord on your computer. However, the overseas correspondent,
who created this particular document, had used English (US)
language settings. Consequently, those settings were "embedded"
within the original document.
If this happens again, try the following simple "fix", .
Open the file in WinWord.
Then, click on "Edit" / "Select All" (or press Ctrl/A).
Click on "Tools" / "Language" / "Select Language".
Change the language to English (UK)
Save the document.
Next time you open the file, WinWord will recognise it as an
English (UK) language document - and will apply the appropriate
spellchecker.
Incidentally, you can apply the same principle to individual
foreign word (or words) within an English language document. For
instance, if you type "Besancon", your English spellchecker will
not recognise the word in any shape or form. Then, if you select
the foreign word and change the language to French, the French
spellchecker should suggest the correct spelling of the city as
Besançon (with a cedilla beneath the letter "c").
(To check spellings in foreign languages, you might need to
install additional spellchecker files. However, the French and
Spanish spellcheckers are usually included with UK versions of
WinWord).
On a slightly different topic, you will probably find that the
page settings of your correspondent's document were based upon
American paper sizes - which might not fit properly onto sheets
of A4 paper. You can solve printing problems by opening the
file, changing the page settings, and re-saving the document.
