File Manager includes an Associate dialog box that makes it possible for users to associate a filename extension with a specific application. File Manager stores these associations in the registration database and the WIN.INI initialization file. If a file has a filename extension that has been associated with an application, that application starts automatically whenever a user double-clicks that file in File Manager.
Using the FindExecutable and ShellExecute functions, applications can take advantage of such associations to find and start applications or open and print files.
An application can use the FindExecutable function to retrieve the name and handle of the executable file that is associated with a specified filename. The ShellExecute function either opens or prints a specified file, depending on the value of its lpszOp parameter. To open a document file, the function relies on the association of the filename extension.