Before submitting a document that you created with Zotero, you should always unlink Zotero citations so that only flat text is left in the document. This avoids distracting highlights and can prevent problems with publishing pipelines.

Always unlink citations in a copy of the document. Keep the original version of the document with active Zotero citations so that, if you need to make changes in response to comments (or even, say, reformat the document in another citation style), you can do so.

To unlink citations with Zotero, simply use the plugin's Unlink Citations button in your copy of the document.

If for some reason you're not able to use Zotero to unlink citations, you can unlink citations directly in Microsoft Word. In a copy of the document, select all text (Ctrl-A/Cmd-A) and press Ctrl-Shift-F9/Cmd-Shift-Fn-F9. (On a Mac, you can also press Cmd-6.)

If you have a document in Google Docs that you're unable to unlink with Zotero, you can download it as a .docx, open it in Word, and perform the same step.

Note that this method will flatten all fields in the document, not just Zotero citations.