How to Read a REG File and Check If It’s Safe Apr 28, 2021, 8:00 am EDT | 3 min read On Windows, a .reg file contains a list of changes to the Windows Registry. These files are a quick way to make simple changes—but they can also be dangerous. Here’s how to see what a REG file does before you run it. What Is a REG File? The Windows Registry is a database where Windows and some third-party applications store settings and other data. Many options on Windows 10 can only be changed in the Windows Registry. Some options can also be changed in Group Policy—but only Professional, Enterprise, and Education editions of Windows 10 have access to that.