That depends a bit on what you mean by "compatible". The general
answer is yes.
The file format is the same in Word 97 and all later versions (so
far).
If you write documents in Word 97, you can open and edit them in any
later version. No conversion is needed. (This ignores occasional
reports in the newsgroups that some documents in some later versions
don't keep proper formatting. I suspect those documents were
'slightly' corrupted, and that the newer version doesn't ignore the
problems.)
If you use new features in later versions, for the most part they
degrade gracefully when you open the document in Word 97. For example,
Word 2000 introduced "nested" tables, where an entire table can be
inside one cell of another table. If you open that document in Word
97, the contents of the inner table will be dumped as plain paragraphs
in the one cell of the outer table. The text is intact but the
formatting isn't. Other features aren't so benign; for example, in
macros, VBA commands from later versions cause errors if they don't
exist in Word 97.
All the later versions have an option in Tools > Options > Save to
turn off features introduced after Word 97, so you can be sure the
document is backward-compatible.
