How, specifically, did you format the document in the first place? If you mean that you selected text and changed the formatting of the selection, the underlying default formatting may resurface during editing.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional

Seems it does occur most frequently when it is just a selected area that has been modified. When this happens, I walk the recipient through changing his normal.dotx defaults to Arial 10pt, single spacing. Is there a way to correct this without having each end user redefine the normal.dotx?

However, it also occurs to paragraphs and parts of paragraphs that have been formatted using styles. This, I don't have a fix for yet.

Is the option to "Automatically update document styles" selected in the Templates and Add-Ins dialog box, for the affected document? If not, formatting in the Normal template will NOT be copied into an existing document.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional

When I bring in a Styles template I've created, I have Automatically update styles checked.

I do not have Automatically update selected for each style in the document.

Did that make sense?

"Automatically update document styles" is required if you want Word to update the styles in a document after you have attached a (new) template to the document. However, once you have done that, you should clear the option again. Otherwise, Word will continue to update styles the next time you open that same document, and you may not want that to happen.

The "Update automatically" option for individual paragraph styles is different. It can be used to incorporate direct formatting into a style.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional