There is only one file type that uses the .MUN extension:
Windows System Resource Archive
A MUN file is a compressed file that contains Windows system resources, including the icons used by a system-level Windows program. Most MUN files are found in the C:/Windows/SystemResources directory, though some are found in application-specific directories. Typically, MUN files have filenames that end in .exe.mun or .dll.mun.
If you are simply looking to access and save a copy of the icons stored within a MUN file, you can use Nirsoft IconsExtract to extract MUN icons and save them as .ICO files. To do so, open IconsExtract, select C:/Windows/SystemResources directory., and then browse to and search the
If you want to explore all the files contained within a MUN archive, you can open and explore the archive with 7-Zip. Note, however, that you cannot use 7-Zip to automatically extract the files contained within a MUN archive. You can, however, use it to manually copy the files contained within a MUN file to a new folder.
Updated: July 11, 2020