The Link Fixer Plugin (note the name change from Permalink Finder) detects when WordPress cannot find a permalink. Before it generates the 404 error the plugin tries to locate any posts with similar words. It does this by searching through the database trying to find any of the word values from the bad link. It takes the best match and then, rather than issuing a 404 error, it sends back a redirect to the correct page.
Users will see the page that they are looking for, and search engine spiders will see the 301 redirect and update their databases so that the page appears correctly in searches.
This is especially useful where WordPress removes words like “the” and “a” from the permalink during conversions from Blogger.com accounts. It is also useful for migrations that formerly used extensions such as html and shtml, when WordPress does not.
The configuration panel allows a user to select how the plugin finds a missing page. The plugin counts the number of words that match to a post. By default, a two word match is sufficient to cause a redirect to the found page. False positives are possible, especially if the user selects a one word match. Increasing the number of words, however makes it unlikely that the plugin will ever find a match. You may eliminate numbers from the search. You may specify that a list of common English words like “the”, “and”, “who”, “you”, etc., not be considered in finding the correct permalink.
Optionally, the plugin will redirect hits on index.html, index.htm, and index.shtml to the blog home page. This is useful when a website previously used a non-php home page.
If WordPress detects a 404 error on robots.txt, sitemap.xml, crossdomain.xml, favicon.ico, or apple-touch-icon.png it will provide a default version.
The plugin will also optionally keep track of the last few 404’s or redirects. This is useful to find out what pages are missing or named badly that keep causing 404 errors or forcing redirects.
Support
This plugin is free and I expect nothing in return. Please rate the plugin at: https://wordpress.org/extend/plugins/permalink-finder/
If you wish to support my programming, You can donate or buy my book:
https://www.facebook.com/BlogsEye
Error Message Eyes: A Programmer’s Guide to the Digital Soul
It's really quite good
By 
guidesify on May 23, 2020
You might have issues with PHP7
By 
bugzbrown on October 2, 2018
Sep 2018. Still works fine
By 
superguiman on September 23, 2018
Works perfectly!
By 
soycarlosvargas on October 16, 2016
No support for this plugin anymore
By 
AlexiaCP on September 3, 2016
The vendor has stopped maintaining the plugin.
What he wrote in the comments section on his own site:
The simple solution is to uninstall permalink finder. I do not support it and haven’t for over three years. It is the first plugin that I ever wrote and it is not the easiest plugin to maintain.
Its 2016 and this still works
By 
theIndianNoob on September 3, 2016
I am using the most updated version of Wordpress, and 2 years down the line, this plugin is still working like a charm...Highly recommended
Very good plugin.
By 
onlain-filmi.net on February 8, 2017
The application is very good. I use it recently on my site (onlain-filmi.net) and am very satisfied. I recommend it.
Used on an old blog - I LOVE this!
By 
Jessica (kmurraycreative) on February 8, 2017
I just decided to change the permalink structure from category/post to just the post name, after having had VintageReveries.com up since 2011.
I have a TON of posts.
This plugin is easy to use, and correctly redirects my old pages to the new ones.
I probably could have done this manually in the htaccess file, but this was a quick and easy fix.
5 stars!