There are many compression format to use to archive files for many reasons. Listed below are some compression libraries for C# of popular compression format like Zip, 7z/SevenZip, Rar.
Without the compression tool itself, we can identify the type of compression file by its extension, whether it’s a ZIP, RAR, 7Z, etc.
And the other way is by reading some bytes of the top part of the file. Each compression tool’s type has its own signature, usually in the first some bytes, which we can see if we open the file in Hex View as image above.