Thanks. So you think that working in "no markup" rather than "simple markup," which just puts a margin bar by changed lines, will make a difference? I'll give it a try. It's much easier to edit a clean copy rather than one with all the annotations, so I don't view in full markup, even though I need to retain all the changes.

There's very little in the way of formatting changes per se; that's something the layout designers take care of before the material goes to the printers. Does formatting put a bigger strain on the program than editorial changes?

This particular document is in .docx format, but if there is a big difference, I'll make sure not to use .doc.

Does saving the document in a compatible version make a difference? I never really thought about it, but the save window just says "compatibility with earlier versions." Does that mean there are changes in document type in 2013 compared to 2007 and 2010? Or only with 2003 and earlier?