Final answer:
Protected View is a security feature that opens files in a read-only mode to protect your computer. Only enable editing and open the file if you trust the source; otherwise, keep it in Protected View.
Step-by-step explanation:
When a file is downloaded from the Internet and it opens in Protected View, it is because Microsoft Office has detected potential security concerns. Protected View is a read-only mode where most editing functions are disabled. The purpose of Protected View is to protect your computer from potentially harmful code that could be executed when the document is opened. The decision to enable editing and open the file should be based on whether you trust the source of the file. If you know and trust the source of the file, it is generally safe to click the 'Enable Editing' button. However, if the source is unknown or you were not expecting to receive a file, it is safer to leave the file in Protected View.