With the file extension APLN, InDesign will mark plug-in files in the DTP (Desktop Publishing) solution. With InDesign, for example, you can create print templates and layouts for print products such as flyers, catalogs or brochures.
With APLN files InDesign can be extended by new functionalities. InDesign plugin files are dll files with only modified endings. These are therefore only used under Windows. On the Mac operating system, the plugins usually have the extension InDesignPlugin.
APLN files belong in the 'Plug-ins' folder in the InDesign program folder.
Most often resolving problems with opening APLN files is very simple. Just install an appropriate program that supports such files. All of the listed programs support APLN files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of APLN files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate APLN files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Adobe InDesign applications is not on the list, select "Browse" option in order to manually locate the directory where Adobe InDesign has been installed.
Sometimes problems with opening APLN files may not lie with the application itself, but can arise due to other causes, such as: