Hi Charlie,

I guess you're doing a lot of Find/Replace? Word can be forced to create a
lot of temporary files if you do that, so it can undo all those changes.

You could try if clearing the Undo-buffer now and then helps:
ActiveDocument.UndoClear

And/Or have the macro save the document:
ActiveDocument.Save

If your document is just text (no tables, text boxes, or fields), you could
read the whole text into a string (sText = ActiveDocument.Content.Text), and
try to do as much of the work as possible on the string rather than on the
document.
Say in the string, you find some position you want to insert text (with say
InStr), you can then set a range to that position in the document, and
insert your comment.

If these tips don't help, maybe post some code you use that's too slow...
Regards,
Klaus