An extension can send the following window messages to retrieve relevant information from File Manager. File Manager is guaranteed to respond correctly only to messages sent from the FMExtensionProc function.
| Message | Description |
| FM_GETDRIVEINFO | File Manager returns drive information from the active window. An extension provides a pointer to an FMS_GETDRIVEINFO structure; File Manager fills the structure with drive information. |
| FM_GETFILESEL | File Manager returns information about a selected file from the active File Manager window (either the directory window or the Search Results window). An extension provides a pointer to an FMS_GETFILESEL structure; File Manager fills the structure with file information. |
| FM_GETFILESELLFN | Same as the FM_GETFILESEL message except that the selected file may have a long filename. |
| FM_GETFOCUS | File Manager returns a value that identifies the type of window with input focus. |
| FM_GETSELCOUNT | File Manager returns the count of selected files in the directory and Search Results windows. |
| FM_GETSELCOUNTLFN | Same as the FM_GETSELCOUNT message except that the count includes files with long filenames. |
| FM_REFRESH_WINDOWS | File Manager repaints either its active window or all of its windows. This message is similar to File Manager's Refresh command on the Window menu. |
| FM_RELOAD_EXTENSIONS | File Manager reloads all extensions. First, File Manager unloads all extensions, sending an FMEVENT_UNLOAD message to each extension. Then, it reloads the extensions, sending an FMEVENT_LOAD message to each extension. The FM_RELOAD_EXTENSIONS message allows an extension to uninstall itself by removing its setting from the WINFILE.INI file; this action causes File Manager to reload the remaining extensions. Other applications and programs (for example, installation programs) can also post this message by calling the PostMessage function. |