When printing a Microsoft Word document that contains a watermark created within Word, an issue may occur in which some of the watermark text characters do not print. The issue may occur with only certain printer model while other models do not experience the issue at all.

Please refer to:
https://support.microsoft.com/en-us/office/insert-a-watermark-f90f26a5-2101-4a75-bbfe-f27ef05002de