Can I add a mdimporter file to have new option search in spotlight? In System/Library/spotlight there are several files like " Application.mdimporter " which seems they appropriate searching for spotlight. Can I add any file like them? Is there any way to make files like them? Can I find files of this kind produced with developers?
Yes, you can create your own Spotlight importers.

You can find Apple's documentation here.

The importers don't need to sit in /System/Library/Spotlight that is intended solely for importers that come with the operating system. What usually happens is an application developer will create an importer to support their file formats and include the importer within the application bundle. So, for example, the importers for Pages file formats sit within the Pages app bundle. But you can also drop importers in ~/Library/Spotlight within your own user profile and OSX will find them there.