You can use any web browser, such as Safari or Chrome, to access Facebook on your computer. If you’re not already signed in, enter your Facebook username and password to do so now. This is the mobile web version of Facebook Messenger, so it may look a little funny in your browser. Now you’ll see the last several messages in the conversation. It’s at the top of the conversation. You’ll want to keep clicking it until you can see the part of the conversation you want to save. The steps to do this are a little different depending on your web browser:  Safari or Chrome for macOS: Press ⌘ Command+P to open the Print prompt, then click Open PDF in Preview. Once the document opens in Preview, go to File > Save As and enter a name for your file. Firefox for macOS: Click File at the top of the screen, then select Export as PDF… Type a name for the conversation in the “Save As” box, then click Save. Chrome for Windows: Press Ctrl+P, click Change under the printer name, select Save as PDF, then click Save.

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Write a summary of the previous text in Chinese:
在网页浏览器中，前往 https://www.facebook.com 前往 https://m.facebook.com/messages 点击要导出的对话。 点击查看更早的消息，查看更多消息。 将对话导出为PDF文件。