They may offer themes, custom icons, or interface tweaks not available in the Play Store version.
Such as the ability to download media, view private profiles, or use advanced developer tools. 2. The Golden Rules of Exploring APKs
Installing random .apk files can lead to malware infections or data theft. Only install apps from trusted sources, and never enter personal banking or sensitive login information into a modded application.
To give you a more interesting and specific guide, could you tell me: did you download this file from (website/forum)?
To find what X_PLUS_00.apk specifically does, you must find its context.
