You're here because you have a file that has a file extension ending in .aca. Files with the file extension .aca can only be launched by certain applications. It's possible that .aca files are data files rather than documents or media, which means they're not meant to be viewed at all.

Files stored in the ACA format are data files created and used by the Microsoft Agent software, and this application is for creating animated characters with interactive functionalities. When a Microsoft Agent output file is accessed by a user, this application locates the associated ACA file and retrieves the data stored in the file to reference those details and provide the user with the functionalities integrated by the author of the output project file. These details are relevant for the application to determine the movement, speech and background audio needed to be displayed. Since these ACA files are Agent Character Animation files, it is created by Microsoft Agent with another file in a different format, and this file is associated to the profile data of the animated character. These ACA files can also be opened and edited using the Microsoft Agent Character Editor software. Users of Microsoft Windows-based systems can install the Microsoft Agent application and the Microsoft Agent Character Editor software to access the functions integrated into these programs and implement support into their systems for these ACA files. However, Microsoft Corporation has as of this writing discontinued support for Microsoft Agent and Microsoft Agent Character Editor in the Microsoft Windows 7 OS.

Launch a .aca file, or any other file on your PC, by double-clicking it. If your file associations are set up correctly, the application that's meant to open your .aca file will open it. It's possible you may need to download or purchase the correct application. It's also possible that you have the correct application on your PC, but .aca files aren't yet associated with it. In this case, when you try to open a .aca file, you can tell Windows which application is the correct one for that file. From then on, opening a  .aca file will open the correct application. Click here to fix .aca file association errors

Be careful not to rename the extension on .aca files, or any other files. This will not change the file type. Only special conversion software can change a file from one file type to another.

A file extension is the set of three or four characters at the end of a filename; in this case, .aca. File extensions tell you what type of file it is, and tell Windows what programs can open it. Windows often associates a default program to each file extension, so that when you double-click the file, the program launches automatically. When that program is no longer on your PC, you can sometimes get an error when you try to open the associated file.