Open the document, file, or web page that you'd like to save in PDF format. It's in the menu bar at the top-left of your screen. It's near the bottom of the drop-down menu. It's in the lower-left corner of the print dialog box. A pop-up menu will open.  If you don't see this option, look for and click on Print using system dialog.... Some applications, such as Adobe Acrobat Reader DC, do not support printing to PDF. It's near the top of the pop-up menu. Do so in the "Save As:" field at the top of the dialog box. Use the drop-down menu below the "Save As:" field or choose a location from the "Favorites" section on the left side of the dialog box. It's the lower-right corner of the dialog box. The document will be saved as a PDF file in the location you specified.

TL;DR in Chinese:
打开文档。 点击文件按钮。 点击打印。 点击PDF按钮，它位于打印对话框的左下角。 点击 另存为PDF。 给文件命名。 选择位置。 点击保存。