First, this is a user to user forum as written at top in image below header line. It looks like you want help from support of IDM Computer Solutions, Inc. which you can get by email as written in help on page opened by clicking on help tab Contents on list item Sales and Support on sublist item Technical Support or using the form on Support - Tech Support page.

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The file association of any file extension with UltraEdit application works as long as being done because UltraEdit for Windows v24.20.0.62 is not involved in file association process at all. This is done by using only Windows built-in features and works as it works for all applications as long as not expecting special features which only a few applications support.

UltraEdit for Windows has the button System File Associations at Advanced - Settings or Configuration - File associations since v24.10 which opens the standard Windows dialog window to associate any file extension with any application. That is like clicking in Windows Control Panel on Default Programs and next on Associate a file type or protocol with a specific program.

UltraEdit for Windows has additionally the check box item Integrate with Explorer as and edit field for context menu name at Advanced - Settings or Configuration - File associations which can be checked to register the UltraEdit shell extension(s) for current user to be able to click with secondary (right) mouse button on any file in Windows Explorer or any other application loading also the Explorer shell extension to open the context menu and next with primary (left) mouse button on the context menu item UltraEdit to open the file in UltraEdit. This method works also for all files currently selected files on using the context menu item.

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Method 1 is clicking in context menu in submenu Open with on Choose default program...

The next steps are:

1. Click on [+] symbol of Other Programs containing UltraEdit Professional Text/Hex Editor.
   UltraEdit is listed here because it has added the registry key HKEY_CURRENT_USER\Software\Classes\Applications\uedit64.exe (64-bit UE) or HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe (32-bit) with the appropriate subkeys and values on first start by current user if no other application has prevented UltraEdit doing this and no registry cleaner application has removed this key with its subkeys and values.
2. Click once with primary (left) mouse button on UltraEdit Professional Text/Hex Editor to select UltraEdit.
3. Click on check box item Always use the selected program to open this kind of file to check it if it is not already checked as by default.
4. Click on button OK.

I made these steps on Windows 7 x64 using my user account and Windows (not installed 32-bit UltraEdit) added to Windows registry the key HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.txt\UserChoice with the string value Progid with string Applications\uedit32.exe. And that's it. The real file association of file extension .txt with Windows Notepad is not modified by Windows. I don't have a computer running Windows 10 to look on what is changed by Windows 10 on user chooses an application as default application for a file with a specific file extension.

Here is the registry export of application registration of 32-bit UltraEdit installed into default program files folder for x86 applications for all users for completeness in case of registry is partly corrupt:

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe]

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe\shell]

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe\shell\edit]

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe\shell\edit\Command]
@="\"C:\\Program Files (x86)\\IDM Computer Solutions\\UltraEdit\\uedit32.exe\" \"%1\""

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe\shell\open]

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe\shell\open\Command]
@="\"C:\\Program Files (x86)\\IDM Computer Solutions\\UltraEdit\\uedit32.exe\" \"%1\""

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe\shell\print]

[HKEY_CURRENT_USER\Software\Classes\Applications\uedit32.exe\shell\print\Command]
@="\"C:\\Program Files (x86)\\IDM Computer Solutions\\UltraEdit\\uedit32.exe\" /p \"%1\""

After doing this I could double click on any *.txt file in Windows Explorer and Total Commander to open the file in UltraEdit.

So if that does not work on your computer, there is something wrong with your registry or an application prevents Windows to add the registry key and the string value. You could use the free Sysinternals tool Process Monitor to find out why the user choice override for standard file association for your user account does not work as expected by you.

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Method 2 is opening Windows Control Panel (also available on Windows 10) and clicking on Default Programs and next on Associate a file type or protocol with a specific program.

The next steps are:

1. Click into the list and type quickly .txt to jump to list entry for file extension .txt or use vertical scroll bar and search with eyes for the .txt list entry.
2. Click on button Change program...
3. Click on [+] symbol of Other Programs containing UltraEdit Professional Text/Hex Editor.
4. Click once with primary (left) mouse button on UltraEdit Professional Text/Hex Editor to select UltraEdit.
5. Click on check box item Always use the selected program to open this kind of file to check it if it is not already checked as by default.
6. Click on button OK.

The steps from third step are the same as those of method 1 because of same Windows dialog. Therefore the modification in Windows registry is the same as on using first method.

UltraEdit is again not involved in file association process done by Windows. So if this file association method being in real the same as method 1 does not work on your computer for your user account, it is not the fault of UltraEdit.

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Why is UltraEdit not listed in programs list after clicking in Windows Control Panel on Default Programs and next on Set Default Programs?

UltraEdit does not register itself as registered application, i.e. it does not add a string value UltraEdit to registry key HKEY_LOCAL_MACHINE\Software\RegisteredApplications with a reference to a Capabilities registry key having a subkey FileAssocations with string values with names being file extensions and with class name as string value.

I don't know the reasons, but I suppose:

1. This registration requires elevated permissions of a local administrator which means it could be done only if UltraEdit is installed for all users of the Windows computer with a user account which belongs to local administrator group and not only for current user as also possible even with no local administrator privileges.
2. UltraEdit is a general text editor which can be used to edit any text file. There are several hundred file extensions for text files. And UltraEdit has also a hex editing mode and therefore can be used to edit any file in hex edit mode. So it would be quite difficult to determine the list of file extensions which by default should be associated with UltraEdit on making use of this Windows feature.

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Microsoft documentation pages which should be read by people interested on file associations on Windows:

• File Types and File Associations
• Default Programs
• Managing Default Applications
• Set program access and computer defaults

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PS: I do not often change file associations, but when I need to do it, I do it most often directly in Windows registry with regedit.exe because of Microsoft removed the GUI interfaces giving a user full control above file associations as in Windows XP and former versions of Windows.

You would have just let me know that you really want to overwrite the file association of file extension .txt with Windows Notepad for all users of a machine (HKEY_LOCAL_MACHINE\Software\Classes) or just current user (HKEY_CURRENT_USER\Software\Classes) with resulting configuration for current user being HKEY_CLASSES_ROOT and I would have offered a batch file for doing this on which the user would need to enter just the file extensions and answer a prompt on doing the file association(s) for current user or entire machine. Windows itself does not offer anymore a GUI interface for doing that as I wrote in my postscript in my previous post since Windows Vista, I guess for security reasons or because of too many users not knowing what they are doing destroyed the correct file association with something which can't work. Windows never supported an undo for a file association made by the user.

Microsoft has just added multiple methods on how to overrule a file association without modifying the real file association. Every user can for his user account overrule the real file association for a file extension on using only GUI interface. For really changing or adding a file association it is necessary to use either Regedit or use command line tools working since Windows 95 and Windows NT4 for people knowing what they are doing (and nowadays have the necessary permissions to do the file associations for an entire machine).