Which action will change how a file behaves in Windows Explorer?

Changing the file extension alters how Windows Explorer interprets and interacts with the file. In Windows, file extensions are part of the file naming convention, and they inform the operating system about the file type and the associated application to open the file. For instance, a file named "document.txt" will be opened by a text editor, while changing the extension to "document.docx" will prompt Windows Explorer to attempt to open it with a word processor.

When the file extension is altered, the behavior of the file can change significantly; the file may appear to be a different type or may not open at all if the corresponding application isn't compatible with the modified extension. This feature is why users can sometimes run into issues, as it can lead to confusion about file types and functionality.

Other actions, while they may affect the content or technical specifications of the file, do not necessarily change how Windows Explorer categorizes or manages the file. For example, editing the file's header or changing the magic number might affect how the file operates internally but won’t change its outward file behavior or the program associated with it. Renaming the file will alter its name but typically doesn't affect how the file is recognized by the operating system unless the extension is also changed.