I know this is a very basic question, but I couldn't find the answer. When I right click on a file with extension .abc and click on Properties and then Change..., then even when I click on Browse... and then on Other Applications, I cannot find the application corresponding to the executable I want to associate with the extension. So, I tried taking the following steps, but no luck:

Here are the steps I took:

  1. I've found the path to the executable which I want to associate with the given file extension (for instance C:\Users\JohnDoe\Desktop\MyPrograms\ABCApp.exe may be such a path if ABCApp.exe is the application I want to use to open files with the .abc extension).

  2. I've navigated to Start>Control Panel>Programs>Default Programs>Set Associations, and tried to add the .abc extension and the associated executable to the list, but this window will only allow me to change the executable used to open an already registered extension. But I want to register a new extension and its executable.

I've found some posts on the internet saying I need to modify the registry with regedit.exe in order to register the extension, but I'm a bit fuzzy with the steps. Could someone please clearly explain what I need to do?


UPDATE: Since the .abc extension is not registered with Windows, it is not possible to choose Open With when one right-clicks on an example.abc file. The following screenshots show the difference betweeen the context menu displayed by right-clicking on an application desktop icon when (1): the application is not registered with Windows, versus when (2): the application is registered with Windows (in my localized version of Windows, Apri means Open and Apri con mans Open With):

  • Registered app's right-click context menu:

    registered app

  • Unregistered app's right-click context menu:

    unregistered app

UPDATE: I've tried the solution posted by @meatspace below, but I get the following error:

I've tried your answer:

C:\> assoc .abc

C:\> ftype ABCApp.SpecialFileType.14=C:\Users\JohnDoe\Desktop\ABC\ABCApp.exe
The file type 'ABCApp.SpecialFileType.14' was not found or there were no associated commands


Exactly how can I create the needed regedit.exe key, if that is the only solution? (Not sure if the dots get translated into subdirectories or not in regedit and how to name the path to the key).



At a command prompt, using .abc from your example:

assoc .abc

Assume it yields .abc = abcfile

Then, at command prompt:

ftype abcfile=C:\path\to\desired\executable.exe

Also, the reason you can't find .abc in Start>Control Panel>Programs>Default Programs>Set Associations is because there is no .abc key in HKEY_CLASSES_ROOT. If HKEY_CLASS_ROOT\abcfile\shell\open\command existed, the key in \command would point to the executable that runs when a file of type .abc is invoked.

  • I've tried your answer, but it did not work. I've updated my post. Could you please check the comments at the bottom of my post and let me know what I should do? Thanks. Jan 25 '15 at 13:48
  • Any idea why I've encountered the problem I've mentioned in my updated post? Thanks. Jan 27 '15 at 21:33
  • 1
    What were the outputs when running assoc and ftype?
    – meatspace
    Jan 27 '15 at 21:52
  • assoc .abc yields .abc=ABCApp.SpecialFileType.14 and type ABCApp.SpecialFileType.14=C:\Users\JohnDoe\Desktop\ABC\ABCApp.exe yields The file type 'ABCApp.SpecialFileType.14' was not found or there were no associated commands. This is what the messages say in my localized version of Windows. Any ideas where the problem may be? Thanks. Jan 27 '15 at 22:18

From the research I've done, .abc file extensions are music notation files, and ABCApp.exe is a program from SONAR use to open, view, and edit those files. You may need to install the ABCApp program first, therefore registering the .abc extension, and probably automatically making the association. You may also want to check this out http://fileinfo.com/extension/abc You may find a better program to do what you want to do.

  • .abc is an example.
    – meatspace
    Jan 25 '15 at 2:56
  • Thank you for your answer. My problem however is that I have an excutable which didn't/won't register with Windows; perhaps the executable's program's installation script was not well written (NOTE: this is very likely the case, as the program I am using is one I didn't purchase, but I nevertheless need it because it does stuff other programs won't do). So, how can I fix this problem? Thanks!!! Jan 25 '15 at 12:35
  • 1
    If you know the exact location/path to the .exe program you want to use to open the .abc file, right click the .abc file, select "open with", then select "choose default program", you can then browse to the location of the .exe program. Once you have chosen a default program for the .abc file extensions, windows should register the extension. Perhaps even selecting to open the .abc file with another program, even though it won't open it, will at least register the extension in Windows, and then you can use the Default Programs app to change the association to your preferred program.
    – Michael
    Jan 25 '15 at 13:05
  • Thanks, but this method does not work because the app is not registered with windows. I've updated my post to explain this. Jan 25 '15 at 13:37
  • 1
    You could simply create a shortcut to your .exe program on your desktop. Attempt to open the .abc file, then browse to the desktop shortcut.
    – Michael
    Jan 25 '15 at 13:45

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