To fix the “not a valid file name” error, remove all special characters from the file name that aren’t valid in Outlook. Also, look for any spaces before or after the file name.

File Extensions are important for an operating system as they tell about the file format. This article covers what are File Extensions and why are they important.

An APK file is an archive of all of the assets an Android app needs to install and run, including not just its main code but things like certificates, resources, and a manifest file.