There are two types of 404 Not Found Errors.We are listed them and given solutions in an easy way by keeping beginners in our mind.This 404 error page appears when there is a problem with post link or page link and if there is a problem with the uploaded media link. Let us go with first problem.
1.Problem with Post/Page link
This error will occur maximum when you did something to your .htaccess file in root folder.It happens only when you renaming the .htaccess file and when you delete the file or when you changing the previous Rewrite rules in .htaccess file.The 404 error page will looks as shown in below image.
This 404 error makes your site traffic to down.You can fix this error by simply writing Rewrite rules into your .htaccess file by logging into your FTP account.If you don’t have this file or deleted due to some other reasons,then simply login to your wordpress dashboard ,then go to Settings>>Permalinks,then click on Save Changes button. See below image for more clarity.Now it will create a default .htaccess file in root directory.
2.Problem with Uploaded file link
If you are not able to read the uploaded files(pdf, image,etc) by browsing their links then you simply delete the .htaccess file in your wp-include.This error comes when your .htaccess file is stopping the file read permissions.To know about which kind of files are being stopped ,edit .htaccess file located in wp-includes directory.There you will be knowing that all extensions which are being stopped or allowed.So,simply delete the .htaccess file or add file extensions in that .htaccess file.It will fix the 404 error(Not Found Error) when you browse the uploaded pdf’s or images.