When you are in WordPress looking for WordPress error 404 in all content or web pages of your website, in typical means denotes the problem with permalinks of your WordPress website.
Fixing process of this error include the following steps:
1.First of all, go to settings
2.Then go to permalinks, and then click save changes button.
3.Doing this, flush write rules and permalink settings will automatically update.
4.In plenty of cases, the concerned problem is fixed with ease.
In some conditions, the situation does not go fair; then it requires manual updating of your .htaccess files. To make these changes, you need to log in to your server with the use of FTP. To make file writable, you can change permissions to 666. After repeating the original solution, you need to again change back permission to 660. This code can manually add to .htaccess file.
Most conditions, trying the above steps your issue resolves. Expert assistance always provides you with an upper hand if things are not clear while troubleshooting the issue.