If "Allow editors to turn on/off watermark of the page" is enabled in watermark settings, there will be a check box of “Display Watermark“ when editing a page.
Administrators are able to maintain the list of pages which do not display the watermark.
Click “Pages without watermark“ and check/uncheck pages in the dialog to hide/show its watermark.
When “Show watermark in attachment preview“ is enabled, if a page does not display watermark, neither do the preview interfaces of its attachments.
Whether the exported word / PDF has a watermark is not affected by whether the watermark is displayed on the page, nor “Export PDF or Word with extra watermark settings” enabled.