Hi Ken,

about the UndoClear-method,
I think, as Word was originally designed IMHO as an
ordinary office-application for small documents,
UndoClear may not clear anything but only set a flag
for, lets say, "disregard" something,
trading speed for slow reliability.

There was once an unknown barrier of complexity,
which Word just couldn't handle anymore.
Maybe it is still there.

I'd try to split up all that editing in single steps.
SaveAs doc-000.doc.
Do Step 1
SaveAs doc-001.doc.
Do step 2
SaveAS doc-002.doc.

Sure, slow and not that easy.

To the best of my knowledge.

What I can add to Helmut's suggestion isn't from real knowledge but
guesswork based on little clues.

According to http://support.microsoft.com/?kbid=211632, a temp file that
starts with ~WRS is a "scratch file". Its description is:

~~~~
When Word runs out of internal random access memory (RAM), it always creates
a single temporary scratch file in the Temp directory to hold information.
This scratch file holds information that is swapped out from the Word
internal file cache, which is allocated from global system memory. The
scratch file varies in size from 64 kilobytes (KB) to 3.5 megabytes (MB).
~~~~

This is where the guesswork comes in: Although it's true that the Undo
buffer is internal to Word, I don't know whether it's part of the internal
file cache that overflows into the scratch file. I also don't know whether
Word has code to shrink the scratch file when the overflow is reduced, or
whether it only grows until the document is closed and the temp file is
discarded.

If Helmut's suggestion of periodically saving the document doesn't help,
then try periodically closing and reopening the document. I'd also be
looking hard at the macro to see whether the amount of editing it does can
be reduced. For example, if you're deleting a group of adjacent paragraphs,
try not to delete them one at a time.