Site visitors will usually see a 404 error page if they visit a site page which has been deleted. Links to the deleted pages may still be on your site or on search results. Search engines may continue to have links to the deleted pages until they index your site again.
Note: You can request the removal of outdated content on this Google Search Console page.
Another reason visitors may see a 404 error page is if links to an active page do not include the page's file extension. File extensions include .htm, .html, and .php.
For example, if visitors see a 404 error page when clicking a link going to mywebsite.com/aboutus, you should edit the link so it takes them to mywebsite.com/aboutus.html. Important: Make sure you are adding the correct file extension.
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