Why is the file called blank.html — what’s its purpose?
The file named Content://Cz.Mobilesoft.Appblock.Fileprovider/Cache/Blank.Html is usually a placeholder. AppBlock and other apps create such blank files when they have to load/test something in the background. It is named blank.html; therefore, none of its contents are displayed to the user. It has nothing to open; it just supports the functions of the app. It is harmless, and it is just how the app quietly runs on your device.

Know more: http://gadgetbyte.net/content-cz-mobilesoft-appblock-fileprovider-cache-blank-html/