Windows 10: Unused File Extension

Once in a while I run CCleaner.
When running Registry cleaner I encounter several "Unused File Extensions" entries.
What app create these entries and why?
thanks for any answer.

:)

 

can't change folder name

if you change a file name extension may become unusable

 

When will Microsoft Edge allow file extensions?

As the title states, When will Edge allow file extensions such as Nortons Vault, Etc.

Also, Since I cannot use edge, Why does internet explorer 11constantly crash, freeze or otherwise become unusable?

 

These are file extensions that are no longer used, as they may have been associated with removed Malware, or other programs that have been uninstalled, deleted or no longer used.
However, we do not suggest using CCleaner's Registry Cleaner, or any other Registry Cleaner or Optimizer software for that matter. These usually cause more problems then they fix. Many of the threads on here start with "I ran this Registry Cleaner and now my computer won't...."

 

Sometimes they are just text files that have the same name, but the extensions(letters assigned after the period/point) are different, so a program can call up the subroutine.

Like:

Routine dothis
call up dothis.xyz
if dothis.xyz =0
then call dothis.abc
if dothis =1
then call dothat.xyz
and so on

You can see this when looking at an installed 3rd party program and copying the file to the desktop and changing the extension to .txt.

Here is an example of a .dll I change to .txt it's not readable though with out another program like Resource Hacker.

 

thanks for your answer and for the advice re registry cleaners in general.
much appreciated.

 

Just to add to the chorus: Never, ever, use any program that claims to "clean" your registry. They always cause more harm than good. There is no need to "clean" the registry.