确保文件扩展名是可见的。 找一个非Word或文本文档的文件。 单击文件选择它，并按⏎ Return。 将当前扩展替换为.docx。 按⏎ Return。 点击使用.docx。

Given the above summary, write a detailed text in English for it.
File extensions are not shown by default. Here's how to enable them now:  Open Finder. Click the Finder menu near the top-left corner of the screen. Click Preferences. Click the Advanced tab (it's the one with the gear). Check the box next to "Show all filename extensions." Click the red circle at the top-left corner of the window to close it. You'll want to start with a file that can't be opened in Word, such as an image file (e.g., .jpeg, .gif, .png) or a sound clip (e.g., .wav, .mp3, .ogg). You'll be using this file to make a fake corrupted Word document. Since you'll be corrupting the file, be sure to choose one you don't care about. You can also make a copy of the file before changing its extension if you wish to preserve it. The file name should now be highlighted in blue, which means its' editable. For example, if you're working with a file called file.jpg, replace ".jpg" with .docx. You'll see a message asking you if you're sure you want to change the file extension. The file is now saved as a .docx file. If you try opening the file in Word, you'll see an error that says it's been corrupted. If you want to hide the file extensions in Finder, return to Finder > Preferences > Advanced and remove the check mark from "Show all filename extensions."