I have a document with multiple paragraphs, each with a centered 4 to 6 line header (format set by boss). I always center the header part and send it out weekly. This time Word takes my centered text and moves it to the left. I center the text, save the document and when I reopen it the header is left justified. Any suggestions?

Use a different Style for your headings (not headers, that is different).

Make sure that your document is not set to update styles from the template. This is under the Developer Tab under the Document Template button.

Using Styles for your formatting gets you you way ahead of the game.
Understanding Styles in Microsoft Word

See if the option to "Automatically open document styles" is selected in the Templates and Add-Ins dialog box. Clear the option and then redefine the style.

To open the dialog box: Click the Office button and then click Word Options. In the Add-Ins category, select "Templates" in the "Manage" drop down and click Go.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional

Thanks Charles and Stefan; Open document styles was NOT on, but you put me on the right track. The source document (which I update each week) had been modified to a left justified style. Eliminating that section solved my problem. Also thanks for leading me to styles. Can't use them on this document but looks interesting for others. Al

You are welcome. You are mistaken, though, in saying you can't use them in your current project. You can use Styles in any document. Word is using Styles whether you know it or not; they are at the heart of Word. If you aren't using them knowingly, chances are that it seems like Word is playing tricks with your document when it uses them.